@@ -169,7 +169,7 @@ class DynamoDBConnection(AWSQueryConnection):
                     break
 
         # Only set host if it isn't manually overwritten
-        if 'host' not in kwargs:
+        if kwargs.get('host') is None:
             kwargs['host'] = region.endpoint
 
         super(DynamoDBConnection, self).__init__(**kwargs)
# Copyright (c) 2014 Amazon.com, Inc. or its affiliates.  All Rights Reserved
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from binascii import crc32

import boto
from boto.compat import json
from boto.connection import AWSQueryConnection
from boto.regioninfo import RegionInfo
from boto.exception import JSONResponseError
from boto.dynamodb2 import exceptions


class DynamoDBConnection(AWSQueryConnection):
    """
    Amazon DynamoDB
    **Overview**

    This is the Amazon DynamoDB API Reference. This guide provides
    descriptions and samples of the low-level DynamoDB API. For
    information about DynamoDB application development, go to the
    `Amazon DynamoDB Developer Guide`_.

    Instead of making the requests to the low-level DynamoDB API
    directly from your application, we recommend that you use the AWS
    Software Development Kits (SDKs). The easy-to-use libraries in the
    AWS SDKs make it unnecessary to call the low-level DynamoDB API
    directly from your application. The libraries take care of request
    authentication, serialization, and connection management. For more
    information, go to `Using the AWS SDKs with DynamoDB`_ in the
    Amazon DynamoDB Developer Guide .

    If you decide to code against the low-level DynamoDB API directly,
    you will need to write the necessary code to authenticate your
    requests. For more information on signing your requests, go to
    `Using the DynamoDB API`_ in the Amazon DynamoDB Developer Guide .

    The following are short descriptions of each low-level API action,
    organized by function.

    **Managing Tables**


    + CreateTable - Creates a table with user-specified provisioned
      throughput settings. You must designate one attribute as the hash
      primary key for the table; you can optionally designate a second
      attribute as the range primary key. DynamoDB creates indexes on
      these key attributes for fast data access. Optionally, you can
      create one or more secondary indexes, which provide fast data
      access using non-key attributes.
    + DescribeTable - Returns metadata for a table, such as table
      size, status, and index information.
    + UpdateTable - Modifies the provisioned throughput settings for a
      table. Optionally, you can modify the provisioned throughput
      settings for global secondary indexes on the table.
    + ListTables - Returns a list of all tables associated with the
      current AWS account and endpoint.
    + DeleteTable - Deletes a table and all of its indexes.


    For conceptual information about managing tables, go to `Working
    with Tables`_ in the Amazon DynamoDB Developer Guide .

    **Reading Data**


    + GetItem - Returns a set of attributes for the item that has a
      given primary key. By default, GetItem performs an eventually
      consistent read; however, applications can specify a strongly
      consistent read instead.
    + BatchGetItem - Performs multiple GetItem requests for data items
      using their primary keys, from one table or multiple tables. The
      response from BatchGetItem has a size limit of 16 MB and returns a
      maximum of 100 items. Both eventually consistent and strongly
      consistent reads can be used.
    + Query - Returns one or more items from a table or a secondary
      index. You must provide a specific hash key value. You can narrow
      the scope of the query using comparison operators against a range
      key value, or on the index key. Query supports either eventual or
      strong consistency. A single response has a size limit of 1 MB.
    + Scan - Reads every item in a table; the result set is eventually
      consistent. You can limit the number of items returned by
      filtering the data attributes, using conditional expressions. Scan
      can be used to enable ad-hoc querying of a table against non-key
      attributes; however, since this is a full table scan without using
      an index, Scan should not be used for any application query use
      case that requires predictable performance.


    For conceptual information about reading data, go to `Working with
    Items`_ and `Query and Scan Operations`_ in the Amazon DynamoDB
    Developer Guide .

    **Modifying Data**


    + PutItem - Creates a new item, or replaces an existing item with
      a new item (including all the attributes). By default, if an item
      in the table already exists with the same primary key, the new
      item completely replaces the existing item. You can use
      conditional operators to replace an item only if its attribute
      values match certain conditions, or to insert a new item only if
      that item doesn't already exist.
    + UpdateItem - Modifies the attributes of an existing item. You
      can also use conditional operators to perform an update only if
      the item's attribute values match certain conditions.
    + DeleteItem - Deletes an item in a table by primary key. You can
      use conditional operators to perform a delete an item only if the
      item's attribute values match certain conditions.
    + BatchWriteItem - Performs multiple PutItem and DeleteItem
      requests across multiple tables in a single request. A failure of
      any request(s) in the batch will not cause the entire
      BatchWriteItem operation to fail. Supports batches of up to 25
      items to put or delete, with a maximum total request size of 16
      MB.


    For conceptual information about modifying data, go to `Working
    with Items`_ and `Query and Scan Operations`_ in the Amazon
    DynamoDB Developer Guide .
    """
    APIVersion = "2012-08-10"
    DefaultRegionName = "us-east-1"
    DefaultRegionEndpoint = "dynamodb.us-east-1.amazonaws.com"
    ServiceName = "DynamoDB"
    TargetPrefix = "DynamoDB_20120810"
    ResponseError = JSONResponseError

    _faults = {
        "ProvisionedThroughputExceededException": exceptions.ProvisionedThroughputExceededException,
        "LimitExceededException": exceptions.LimitExceededException,
        "ConditionalCheckFailedException": exceptions.ConditionalCheckFailedException,
        "ResourceInUseException": exceptions.ResourceInUseException,
        "ResourceNotFoundException": exceptions.ResourceNotFoundException,
        "InternalServerError": exceptions.InternalServerError,
        "ItemCollectionSizeLimitExceededException": exceptions.ItemCollectionSizeLimitExceededException,
    }

    NumberRetries = 10


    def __init__(self, **kwargs):
        region = kwargs.pop('region', None)
        validate_checksums = kwargs.pop('validate_checksums', True)
        if not region:
            region_name = boto.config.get('DynamoDB', 'region',
                                          self.DefaultRegionName)
            for reg in boto.dynamodb2.regions():
                if reg.name == region_name:
                    region = reg
                    break

        # Only set host if it isn't manually overwritten
        if 'host' not in kwargs:
            kwargs['host'] = region.endpoint

        super(DynamoDBConnection, self).__init__(**kwargs)
        self.region = region
        self._validate_checksums = boto.config.getbool(
            'DynamoDB', 'validate_checksums', validate_checksums)
        self.throughput_exceeded_events = 0

    def _required_auth_capability(self):
        return ['hmac-v4']

    def batch_get_item(self, request_items, return_consumed_capacity=None):
        """
        The BatchGetItem operation returns the attributes of one or
        more items from one or more tables. You identify requested
        items by primary key.

        A single operation can retrieve up to 16 MB of data, which can
        contain as many as 100 items. BatchGetItem will return a
        partial result if the response size limit is exceeded, the
        table's provisioned throughput is exceeded, or an internal
        processing failure occurs. If a partial result is returned,
        the operation returns a value for UnprocessedKeys . You can
        use this value to retry the operation starting with the next
        item to get.

        For example, if you ask to retrieve 100 items, but each
        individual item is 300 KB in size, the system returns 52 items
        (so as not to exceed the 16 MB limit). It also returns an
        appropriate UnprocessedKeys value so you can get the next page
        of results. If desired, your application can include its own
        logic to assemble the pages of results into one data set.

        If none of the items can be processed due to insufficient
        provisioned throughput on all of the tables in the request,
        then BatchGetItem will return a
        ProvisionedThroughputExceededException . If at least one of
        the items is successfully processed, then BatchGetItem
        completes successfully, while returning the keys of the unread
        items in UnprocessedKeys .

        If DynamoDB returns any unprocessed items, you should retry
        the batch operation on those items. However, we strongly
        recommend that you use an exponential backoff algorithm . If
        you retry the batch operation immediately, the underlying read
        or write requests can still fail due to throttling on the
        individual tables. If you delay the batch operation using
        exponential backoff, the individual requests in the batch are
        much more likely to succeed.

        For more information, go to `Batch Operations and Error
        Handling`_ in the Amazon DynamoDB Developer Guide .

        By default, BatchGetItem performs eventually consistent reads
        on every table in the request. If you want strongly consistent
        reads instead, you can set ConsistentRead to `True` for any or
        all tables.

        In order to minimize response latency, BatchGetItem retrieves
        items in parallel.

        When designing your application, keep in mind that DynamoDB
        does not return attributes in any particular order. To help
        parse the response by item, include the primary key values for
        the items in your request in the AttributesToGet parameter.

        If a requested item does not exist, it is not returned in the
        result. Requests for nonexistent items consume the minimum
        read capacity units according to the type of read. For more
        information, see `Capacity Units Calculations`_ in the Amazon
        DynamoDB Developer Guide .

        :type request_items: map
        :param request_items:
        A map of one or more table names and, for each table, the corresponding
            primary keys for the items to retrieve. Each table name can be
            invoked only once.

        Each element in the map consists of the following:


        + Keys - An array of primary key attribute values that define specific
              items in the table. For each primary key, you must provide all of
              the key attributes. For example, with a hash type primary key, you
              only need to specify the hash attribute. For a hash-and-range type
              primary key, you must specify both the hash attribute and the range
              attribute.
        + AttributesToGet - One or more attributes to be retrieved from the
              table. By default, all attributes are returned. If a specified
              attribute is not found, it does not appear in the result. Note that
              AttributesToGet has no effect on provisioned throughput
              consumption. DynamoDB determines capacity units consumed based on
              item size, not on the amount of data that is returned to an
              application.
        + ConsistentRead - If `True`, a strongly consistent read is used; if
              `False` (the default), an eventually consistent read is used.

        :type return_consumed_capacity: string
        :param return_consumed_capacity: A value that if set to `TOTAL`, the
            response includes ConsumedCapacity data for tables and indexes. If
            set to `INDEXES`, the response includes ConsumedCapacity for
            indexes. If set to `NONE` (the default), ConsumedCapacity is not
            included in the response.

        """
        params = {'RequestItems': request_items, }
        if return_consumed_capacity is not None:
            params['ReturnConsumedCapacity'] = return_consumed_capacity
        return self.make_request(action='BatchGetItem',
                                 body=json.dumps(params))

    def batch_write_item(self, request_items, return_consumed_capacity=None,
                         return_item_collection_metrics=None):
        """
        The BatchWriteItem operation puts or deletes multiple items in
        one or more tables. A single call to BatchWriteItem can write
        up to 16 MB of data, which can comprise as many as 25 put or
        delete requests. Individual items to be written can be as
        large as 400 KB.


        BatchWriteItem cannot update items. To update items, use the
        UpdateItem API.


        The individual PutItem and DeleteItem operations specified in
        BatchWriteItem are atomic; however BatchWriteItem as a whole
        is not. If any requested operations fail because the table's
        provisioned throughput is exceeded or an internal processing
        failure occurs, the failed operations are returned in the
        UnprocessedItems response parameter. You can investigate and
        optionally resend the requests. Typically, you would call
        BatchWriteItem in a loop. Each iteration would check for
        unprocessed items and submit a new BatchWriteItem request with
        those unprocessed items until all items have been processed.

        Note that if none of the items can be processed due to
        insufficient provisioned throughput on all of the tables in
        the request, then BatchWriteItem will return a
        ProvisionedThroughputExceededException .

        If DynamoDB returns any unprocessed items, you should retry
        the batch operation on those items. However, we strongly
        recommend that you use an exponential backoff algorithm . If
        you retry the batch operation immediately, the underlying read
        or write requests can still fail due to throttling on the
        individual tables. If you delay the batch operation using
        exponential backoff, the individual requests in the batch are
        much more likely to succeed.

        For more information, go to `Batch Operations and Error
        Handling`_ in the Amazon DynamoDB Developer Guide .

        With BatchWriteItem , you can efficiently write or delete
        large amounts of data, such as from Amazon Elastic MapReduce
        (EMR), or copy data from another database into DynamoDB. In
        order to improve performance with these large-scale
        operations, BatchWriteItem does not behave in the same way as
        individual PutItem and DeleteItem calls would For example, you
        cannot specify conditions on individual put and delete
        requests, and BatchWriteItem does not return deleted items in
        the response.

        If you use a programming language that supports concurrency,
        such as Java, you can use threads to write items in parallel.
        Your application must include the necessary logic to manage
        the threads. With languages that don't support threading, such
        as PHP, you must update or delete the specified items one at a
        time. In both situations, BatchWriteItem provides an
        alternative where the API performs the specified put and
        delete operations in parallel, giving you the power of the
        thread pool approach without having to introduce complexity
        into your application.

        Parallel processing reduces latency, but each specified put
        and delete request consumes the same number of write capacity
        units whether it is processed in parallel or not. Delete
        operations on nonexistent items consume one write capacity
        unit.

        If one or more of the following is true, DynamoDB rejects the
        entire batch write operation:


        + One or more tables specified in the BatchWriteItem request
          does not exist.
        + Primary key attributes specified on an item in the request
          do not match those in the corresponding table's primary key
          schema.
        + You try to perform multiple operations on the same item in
          the same BatchWriteItem request. For example, you cannot put
          and delete the same item in the same BatchWriteItem request.
        + There are more than 25 requests in the batch.
        + Any individual item in a batch exceeds 400 KB.
        + The total request size exceeds 16 MB.

        :type request_items: map
        :param request_items:
        A map of one or more table names and, for each table, a list of
            operations to be performed ( DeleteRequest or PutRequest ). Each
            element in the map consists of the following:


        + DeleteRequest - Perform a DeleteItem operation on the specified item.
              The item to be deleted is identified by a Key subelement:

            + Key - A map of primary key attribute values that uniquely identify
                  the ! item. Each entry in this map consists of an attribute name
                  and an attribute value. For each primary key, you must provide all
                  of the key attributes. For example, with a hash type primary key,
                  you only need to specify the hash attribute. For a hash-and-range
                  type primary key, you must specify both the hash attribute and the
                  range attribute.

        + PutRequest - Perform a PutItem operation on the specified item. The
              item to be put is identified by an Item subelement:

            + Item - A map of attributes and their values. Each entry in this map
                  consists of an attribute name and an attribute value. Attribute
                  values must not be null; string and binary type attributes must
                  have lengths greater than zero; and set type attributes must not be
                  empty. Requests that contain empty values will be rejected with a
                  ValidationException exception. If you specify any attributes that
                  are part of an index key, then the data types for those attributes
                  must match those of the schema in the table's attribute definition.

        :type return_consumed_capacity: string
        :param return_consumed_capacity: A value that if set to `TOTAL`, the
            response includes ConsumedCapacity data for tables and indexes. If
            set to `INDEXES`, the response includes ConsumedCapacity for
            indexes. If set to `NONE` (the default), ConsumedCapacity is not
            included in the response.

        :type return_item_collection_metrics: string
        :param return_item_collection_metrics: A value that if set to `SIZE`,
            the response includes statistics about item collections, if any,
            that were modified during the operation are returned in the
            response. If set to `NONE` (the default), no statistics are
            returned.

        """
        params = {'RequestItems': request_items, }
        if return_consumed_capacity is not None:
            params['ReturnConsumedCapacity'] = return_consumed_capacity
        if return_item_collection_metrics is not None:
            params['ReturnItemCollectionMetrics'] = return_item_collection_metrics
        return self.make_request(action='BatchWriteItem',
                                 body=json.dumps(params))

    def create_table(self, attribute_definitions, table_name, key_schema,
                     provisioned_throughput, local_secondary_indexes=None,
                     global_secondary_indexes=None):
        """
        The CreateTable operation adds a new table to your account. In
        an AWS account, table names must be unique within each region.
        That is, you can have two tables with same name if you create
        the tables in different regions.

        CreateTable is an asynchronous operation. Upon receiving a
        CreateTable request, DynamoDB immediately returns a response
        with a TableStatus of `CREATING`. After the table is created,
        DynamoDB sets the TableStatus to `ACTIVE`. You can perform
        read and write operations only on an `ACTIVE` table.

        You can optionally define secondary indexes on the new table,
        as part of the CreateTable operation. If you want to create
        multiple tables with secondary indexes on them, you must
        create the tables sequentially. Only one table with secondary
        indexes can be in the `CREATING` state at any given time.

        You can use the DescribeTable API to check the table status.

        :type attribute_definitions: list
        :param attribute_definitions: An array of attributes that describe the
            key schema for the table and indexes.

        :type table_name: string
        :param table_name: The name of the table to create.

        :type key_schema: list
        :param key_schema: Specifies the attributes that make up the primary
            key for a table or an index. The attributes in KeySchema must also
            be defined in the AttributeDefinitions array. For more information,
            see `Data Model`_ in the Amazon DynamoDB Developer Guide .
        Each KeySchemaElement in the array is composed of:


        + AttributeName - The name of this key attribute.
        + KeyType - Determines whether the key attribute is `HASH` or `RANGE`.


        For a primary key that consists of a hash attribute, you must specify
            exactly one element with a KeyType of `HASH`.

        For a primary key that consists of hash and range attributes, you must
            specify exactly two elements, in this order: The first element must
            have a KeyType of `HASH`, and the second element must have a
            KeyType of `RANGE`.

        For more information, see `Specifying the Primary Key`_ in the Amazon
            DynamoDB Developer Guide .

        :type local_secondary_indexes: list
        :param local_secondary_indexes:
        One or more local secondary indexes (the maximum is five) to be created
            on the table. Each index is scoped to a given hash key value. There
            is a 10 GB size limit per hash key; otherwise, the size of a local
            secondary index is unconstrained.

        Each local secondary index in the array includes the following:


        + IndexName - The name of the local secondary index. Must be unique
              only for this table.
        + KeySchema - Specifies the key schema for the local secondary index.
              The key schema must begin with the same hash key attribute as the
              table.
        + Projection - Specifies attributes that are copied (projected) from
              the table into the index. These are in addition to the primary key
              attributes and index key attributes, which are automatically
              projected. Each attribute specification is composed of:

            + ProjectionType - One of the following:

                + `KEYS_ONLY` - Only the index and primary keys are projected into the
                      index.
                + `INCLUDE` - Only the specified table attributes are projected into
                      the index. The list of projected attributes are in NonKeyAttributes
                      .
                + `ALL` - All of the table attributes are projected into the index.

            + NonKeyAttributes - A list of one or more non-key attribute names that
                  are projected into the secondary index. The total count of
                  attributes specified in NonKeyAttributes , summed across all of the
                  secondary indexes, must not exceed 20. If you project the same
                  attribute into two different indexes, this counts as two distinct
                  attributes when determining the total.

        :type global_secondary_indexes: list
        :param global_secondary_indexes:
        One or more global secondary indexes (the maximum is five) to be
            created on the table. Each global secondary index in the array
            includes the following:


        + IndexName - The name of the global secondary index. Must be unique
              only for this table.
        + KeySchema - Specifies the key schema for the global secondary index.
        + Projection - Specifies attributes that are copied (projected) from
              the table into the index. These are in addition to the primary key
              attributes and index key attributes, which are automatically
              projected. Each attribute specification is composed of:

            + ProjectionType - One of the following:

                + `KEYS_ONLY` - Only the index and primary keys are projected into the
                      index.
                + `INCLUDE` - Only the specified table attributes are projected into
                      the index. The list of projected attributes are in NonKeyAttributes
                      .
                + `ALL` - All of the table attributes are projected into the index.

            + NonKeyAttributes - A list of one or more non-key attribute names that
                  are projected into the secondary index. The total count of
                  attributes specified in NonKeyAttributes , summed across all of the
                  secondary indexes, must not exceed 20. If you project the same
                  attribute into two different indexes, this counts as two distinct
                  attributes when determining the total.

        + ProvisionedThroughput - The provisioned throughput settings for the
              global secondary index, consisting of read and write capacity
              units.

        :type provisioned_throughput: dict
        :param provisioned_throughput: Represents the provisioned throughput
            settings for a specified table or index. The settings can be
            modified using the UpdateTable operation.
        For current minimum and maximum provisioned throughput values, see
            `Limits`_ in the Amazon DynamoDB Developer Guide .

        """
        params = {
            'AttributeDefinitions': attribute_definitions,
            'TableName': table_name,
            'KeySchema': key_schema,
            'ProvisionedThroughput': provisioned_throughput,
        }
        if local_secondary_indexes is not None:
            params['LocalSecondaryIndexes'] = local_secondary_indexes
        if global_secondary_indexes is not None:
            params['GlobalSecondaryIndexes'] = global_secondary_indexes
        return self.make_request(action='CreateTable',
                                 body=json.dumps(params))

    def delete_item(self, table_name, key, expected=None,
                    conditional_operator=None, return_values=None,
                    return_consumed_capacity=None,
                    return_item_collection_metrics=None,
                    condition_expression=None,
                    expression_attribute_names=None,
                    expression_attribute_values=None):
        """
        Deletes a single item in a table by primary key. You can
        perform a conditional delete operation that deletes the item
        if it exists, or if it has an expected attribute value.

        In addition to deleting an item, you can also return the
        item's attribute values in the same operation, using the
        ReturnValues parameter.

        Unless you specify conditions, the DeleteItem is an idempotent
        operation; running it multiple times on the same item or
        attribute does not result in an error response.

        Conditional deletes are useful for deleting items only if
        specific conditions are met. If those conditions are met,
        DynamoDB performs the delete. Otherwise, the item is not
        deleted.

        :type table_name: string
        :param table_name: The name of the table from which to delete the item.

        :type key: map
        :param key: A map of attribute names to AttributeValue objects,
            representing the primary key of the item to delete.
        For the primary key, you must provide all of the attributes. For
            example, with a hash type primary key, you only need to specify the
            hash attribute. For a hash-and-range type primary key, you must
            specify both the hash attribute and the range attribute.

        :type expected: map
        :param expected:
        There is a newer parameter available. Use ConditionExpression instead.
            Note that if you use Expected and ConditionExpression at the same
            time, DynamoDB will return a ValidationException exception.

        This parameter does not support lists or maps.

        A map of attribute/condition pairs. Expected provides a conditional
            block for the DeleteItem operation.

        Each element of Expected consists of an attribute name, a comparison
            operator, and one or more values. DynamoDB compares the attribute
            with the value(s) you supplied, using the comparison operator. For
            each Expected element, the result of the evaluation is either true
            or false.

        If you specify more than one element in the Expected map, then by
            default all of the conditions must evaluate to true. In other
            words, the conditions are ANDed together. (You can use the
            ConditionalOperator parameter to OR the conditions instead. If you
            do this, then at least one of the conditions must evaluate to true,
            rather than all of them.)

        If the Expected map evaluates to true, then the conditional operation
            succeeds; otherwise, it fails.

        Expected contains the following:


        + AttributeValueList - One or more values to evaluate against the
              supplied attribute. The number of values in the list depends on the
              ComparisonOperator being used. For type Number, value comparisons
              are numeric. String value comparisons for greater than, equals, or
              less than are based on ASCII character code values. For example,
              `a` is greater than `A`, and `a` is greater than `B`. For a list of
              code values, see
              `http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters`_.
              For type Binary, DynamoDB treats each byte of the binary data as
              unsigned when it compares binary values, for example when
              evaluating query expressions.
        + ComparisonOperator - A comparator for evaluating attributes in the
              AttributeValueList . When performing the comparison, DynamoDB uses
              strongly consistent reads. The following comparison operators are
              available: `EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL |
              CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN` The following
              are descriptions of each comparison operator.

            + `EQ` : Equal. `EQ` is supported for all datatypes, including lists
                and maps. AttributeValueList can contain only one AttributeValue
                element of type String, Number, Binary, String Set, Number Set, or
                Binary Set. If an item contains an AttributeValue element of a
                different type than the one specified in the request, the value
                does not match. For example, `{"S":"6"}` does not equal
                `{"N":"6"}`. Also, `{"N":"6"}` does not equal `{"NS":["6", "2",
                "1"]}`. > <li>
            + `NE` : Not equal. `NE` is supported for all datatypes, including
                lists and maps. AttributeValueList can contain only one
                AttributeValue of type String, Number, Binary, String Set, Number
                Set, or Binary Set. If an item contains an AttributeValue of a
                different type than the one specified in the request, the value
                does not match. For example, `{"S":"6"}` does not equal
                `{"N":"6"}`. Also, `{"N":"6"}` does not equal `{"NS":["6", "2",
                "1"]}`. > <li>
            + `LE` : Less than or equal. AttributeValueList can contain only one
                AttributeValue element of type String, Number, or Binary (not a set
                type). If an item contains an AttributeValue element of a different
                type than the one specified in the request, the value does not
                match. For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `LT` : Less than. AttributeValueList can contain only one
                AttributeValue of type String, Number, or Binary (not a set type).
                If an item contains an AttributeValue element of a different type
                than the one specified in the request, the value does not match.
                For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `GE` : Greater than or equal. AttributeValueList can contain only one
                AttributeValue element of type String, Number, or Binary (not a set
                type). If an item contains an AttributeValue element of a different
                type than the one specified in the request, the value does not
                match. For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `GT` : Greater than. AttributeValueList can contain only one
                AttributeValue element of type String, Number, or Binary (not a set
                type). If an item contains an AttributeValue element of a different
                type than the one specified in the request, the value does not
                match. For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `NOT_NULL` : The attribute exists. `NOT_NULL` is supported for all
                  datatypes, including lists and maps. This operator tests for the
                  existence of an attribute, not its data type. If the data type of
                  attribute " `a`" is null, and you evaluate it using `NOT_NULL`, the
                  result is a Boolean true . This result is because the attribute "
                  `a`" exists; its data type is not relevant to the `NOT_NULL`
                  comparison operator.
            + `NULL` : The attribute does not exist. `NULL` is supported for all
                  datatypes, including lists and maps. This operator tests for the
                  nonexistence of an attribute, not its data type. If the data type
                  of attribute " `a`" is null, and you evaluate it using `NULL`, the
                  result is a Boolean false . This is because the attribute " `a`"
                  exists; its data type is not relevant to the `NULL` comparison
                  operator.
            + `CONTAINS` : Checks for a subsequence, or value in a set.
                  AttributeValueList can contain only one AttributeValue element of
                  type String, Number, or Binary (not a set type). If the target
                  attribute of the comparison is of type String, then the operator
                  checks for a substring match. If the target attribute of the
                  comparison is of type Binary, then the operator looks for a
                  subsequence of the target that matches the input. If the target
                  attribute of the comparison is a set (" `SS`", " `NS`", or "
                  `BS`"), then the operator evaluates to true if it finds an exact
                  match with any member of the set. CONTAINS is supported for lists:
                  When evaluating " `a CONTAINS b`", " `a`" can be a list; however, "
                  `b`" cannot be a set, a map, or a list.
            + `NOT_CONTAINS` : Checks for absence of a subsequence, or absence of a
                  value in a set. AttributeValueList can contain only one
                  AttributeValue element of type String, Number, or Binary (not a set
                  type). If the target attribute of the comparison is a String, then
                  the operator checks for the absence of a substring match. If the
                  target attribute of the comparison is Binary, then the operator
                  checks for the absence of a subsequence of the target that matches
                  the input. If the target attribute of the comparison is a set ("
                  `SS`", " `NS`", or " `BS`"), then the operator evaluates to true if
                  it does not find an exact match with any member of the set.
                  NOT_CONTAINS is supported for lists: When evaluating " `a NOT
                  CONTAINS b`", " `a`" can be a list; however, " `b`" cannot be a
                  set, a map, or a list.
            + `BEGINS_WITH` : Checks for a prefix. AttributeValueList can contain
                only one AttributeValue of type String or Binary (not a Number or a
                set type). The target attribute of the comparison must be of type
                String or Binary (not a Number or a set type). > <li>
            + `IN` : Checks for matching elements within two sets.
                  AttributeValueList can contain one or more AttributeValue elements
                  of type String, Number, or Binary (not a set type). These
                  attributes are compared against an existing set type attribute of
                  an item. If any elements of the input set are present in the item
                  attribute, the expression evaluates to true.
            + `BETWEEN` : Greater than or equal to the first value, and less than
                  or equal to the second value. AttributeValueList must contain two
                  AttributeValue elements of the same type, either String, Number, or
                  Binary (not a set type). A target attribute matches if the target
                  value is greater than, or equal to, the first element and less
                  than, or equal to, the second element. If an item contains an
                  AttributeValue element of a different type than the one specified
                  in the request, the value does not match. For example, `{"S":"6"}`
                  does not compare to `{"N":"6"}`. Also, `{"N":"6"}` does not compare
                  to `{"NS":["6", "2", "1"]}`



        For usage examples of AttributeValueList and ComparisonOperator , see
            `Legacy Conditional Parameters`_ in the Amazon DynamoDB Developer
            Guide .

        For backward compatibility with previous DynamoDB releases, the
            following parameters can be used instead of AttributeValueList and
            ComparisonOperator :


        + Value - A value for DynamoDB to compare with an attribute.
        + Exists - A Boolean value that causes DynamoDB to evaluate the value
              before attempting the conditional operation:

            + If Exists is `True`, DynamoDB will check to see if that attribute
                  value already exists in the table. If it is found, then the
                  condition evaluates to true; otherwise the condition evaluate to
                  false.
            + If Exists is `False`, DynamoDB assumes that the attribute value does
                  not exist in the table. If in fact the value does not exist, then
                  the assumption is valid and the condition evaluates to true. If the
                  value is found, despite the assumption that it does not exist, the
                  condition evaluates to false.
          Note that the default value for Exists is `True`.


        The Value and Exists parameters are incompatible with
            AttributeValueList and ComparisonOperator . Note that if you use
            both sets of parameters at once, DynamoDB will return a
            ValidationException exception.

        :type conditional_operator: string
        :param conditional_operator:
        There is a newer parameter available. Use ConditionExpression instead.
            Note that if you use ConditionalOperator and ConditionExpression at
            the same time, DynamoDB will return a ValidationException
            exception.

        This parameter does not support lists or maps.

        A logical operator to apply to the conditions in the Expected map:


        + `AND` - If all of the conditions evaluate to true, then the entire
              map evaluates to true.
        + `OR` - If at least one of the conditions evaluate to true, then the
              entire map evaluates to true.


        If you omit ConditionalOperator , then `AND` is the default.

        The operation will succeed only if the entire map evaluates to true.

        :type return_values: string
        :param return_values:
        Use ReturnValues if you want to get the item attributes as they
            appeared before they were deleted. For DeleteItem , the valid
            values are:


        + `NONE` - If ReturnValues is not specified, or if its value is `NONE`,
              then nothing is returned. (This setting is the default for
              ReturnValues .)
        + `ALL_OLD` - The content of the old item is returned.

        :type return_consumed_capacity: string
        :param return_consumed_capacity: A value that if set to `TOTAL`, the
            response includes ConsumedCapacity data for tables and indexes. If
            set to `INDEXES`, the response includes ConsumedCapacity for
            indexes. If set to `NONE` (the default), ConsumedCapacity is not
            included in the response.

        :type return_item_collection_metrics: string
        :param return_item_collection_metrics: A value that if set to `SIZE`,
            the response includes statistics about item collections, if any,
            that were modified during the operation are returned in the
            response. If set to `NONE` (the default), no statistics are
            returned.

        :type condition_expression: string
        :param condition_expression: A condition that must be satisfied in
            order for a conditional DeleteItem to succeed.
        An expression can contain any of the following:


        + Boolean functions: `attribute_exists | attribute_not_exists |
              contains | begins_with` These function names are case-sensitive.
        + Comparison operators: ` = | <> | < | > | <=
              | >= | BETWEEN | IN`
        + Logical operators: `AND | OR | NOT`


        For more information on condition expressions, go to `Specifying
            Conditions`_ in the Amazon DynamoDB Developer Guide .

        :type expression_attribute_names: map
        :param expression_attribute_names: One or more substitution tokens for
            simplifying complex expressions. The following are some use cases
            for using ExpressionAttributeNames :

        + To shorten an attribute name that is very long or unwieldy in an
              expression.
        + To create a placeholder for repeating occurrences of an attribute
              name in an expression.
        + To prevent special characters in an attribute name from being
              misinterpreted in an expression.


        Use the **#** character in an expression to dereference an attribute
            name. For example, consider the following expression:


        + `order.customerInfo.LastName = "Smith" OR order.customerInfo.LastName
              = "Jones"`


        Now suppose that you specified the following for
            ExpressionAttributeNames :


        + `{"#name":"order.customerInfo.LastName"}`


        The expression can now be simplified as follows:


        + `#name = "Smith" OR #name = "Jones"`


        For more information on expression attribute names, go to `Accessing
            Item Attributes`_ in the Amazon DynamoDB Developer Guide .

        :type expression_attribute_values: map
        :param expression_attribute_values: One or more values that can be
            substituted in an expression.
        Use the **:** (colon) character in an expression to dereference an
            attribute value. For example, suppose that you wanted to check
            whether the value of the ProductStatus attribute was one of the
            following:

        `Available | Backordered | Discontinued`

        You would first need to specify ExpressionAttributeValues as follows:

        `{ ":avail":{"S":"Available"}, ":back":{"S":"Backordered"},
            ":disc":{"S":"Discontinued"} }`

        You could then use these values in an expression, such as this:

        `ProductStatus IN (:avail, :back, :disc)`

        For more information on expression attribute values, go to `Specifying
            Conditions`_ in the Amazon DynamoDB Developer Guide .

        """
        params = {'TableName': table_name, 'Key': key, }
        if expected is not None:
            params['Expected'] = expected
        if conditional_operator is not None:
            params['ConditionalOperator'] = conditional_operator
        if return_values is not None:
            params['ReturnValues'] = return_values
        if return_consumed_capacity is not None:
            params['ReturnConsumedCapacity'] = return_consumed_capacity
        if return_item_collection_metrics is not None:
            params['ReturnItemCollectionMetrics'] = return_item_collection_metrics
        if condition_expression is not None:
            params['ConditionExpression'] = condition_expression
        if expression_attribute_names is not None:
            params['ExpressionAttributeNames'] = expression_attribute_names
        if expression_attribute_values is not None:
            params['ExpressionAttributeValues'] = expression_attribute_values
        return self.make_request(action='DeleteItem',
                                 body=json.dumps(params))

    def delete_table(self, table_name):
        """
        The DeleteTable operation deletes a table and all of its
        items. After a DeleteTable request, the specified table is in
        the `DELETING` state until DynamoDB completes the deletion. If
        the table is in the `ACTIVE` state, you can delete it. If a
        table is in `CREATING` or `UPDATING` states, then DynamoDB
        returns a ResourceInUseException . If the specified table does
        not exist, DynamoDB returns a ResourceNotFoundException . If
        table is already in the `DELETING` state, no error is
        returned.


        DynamoDB might continue to accept data read and write
        operations, such as GetItem and PutItem , on a table in the
        `DELETING` state until the table deletion is complete.


        When you delete a table, any indexes on that table are also
        deleted.

        Use the DescribeTable API to check the status of the table.

        :type table_name: string
        :param table_name: The name of the table to delete.

        """
        params = {'TableName': table_name, }
        return self.make_request(action='DeleteTable',
                                 body=json.dumps(params))

    def describe_table(self, table_name):
        """
        Returns information about the table, including the current
        status of the table, when it was created, the primary key
        schema, and any indexes on the table.


        If you issue a DescribeTable request immediately after a
        CreateTable request, DynamoDB might return a
        ResourceNotFoundException. This is because DescribeTable uses
        an eventually consistent query, and the metadata for your
        table might not be available at that moment. Wait for a few
        seconds, and then try the DescribeTable request again.

        :type table_name: string
        :param table_name: The name of the table to describe.

        """
        params = {'TableName': table_name, }
        return self.make_request(action='DescribeTable',
                                 body=json.dumps(params))

    def get_item(self, table_name, key, attributes_to_get=None,
                 consistent_read=None, return_consumed_capacity=None,
                 projection_expression=None, expression_attribute_names=None):
        """
        The GetItem operation returns a set of attributes for the item
        with the given primary key. If there is no matching item,
        GetItem does not return any data.

        GetItem provides an eventually consistent read by default. If
        your application requires a strongly consistent read, set
        ConsistentRead to `True`. Although a strongly consistent read
        might take more time than an eventually consistent read, it
        always returns the last updated value.

        :type table_name: string
        :param table_name: The name of the table containing the requested item.

        :type key: map
        :param key: A map of attribute names to AttributeValue objects,
            representing the primary key of the item to retrieve.
        For the primary key, you must provide all of the attributes. For
            example, with a hash type primary key, you only need to specify the
            hash attribute. For a hash-and-range type primary key, you must
            specify both the hash attribute and the range attribute.

        :type attributes_to_get: list
        :param attributes_to_get:
        There is a newer parameter available. Use ProjectionExpression instead.
            Note that if you use AttributesToGet and ProjectionExpression at
            the same time, DynamoDB will return a ValidationException
            exception.

        This parameter allows you to retrieve lists or maps; however, it cannot
            retrieve individual list or map elements.

        The names of one or more attributes to retrieve. If no attribute names
            are specified, then all attributes will be returned. If any of the
            requested attributes are not found, they will not appear in the
            result.

        Note that AttributesToGet has no effect on provisioned throughput
            consumption. DynamoDB determines capacity units consumed based on
            item size, not on the amount of data that is returned to an
            application.

        :type consistent_read: boolean
        :param consistent_read: A value that if set to `True`, then the
            operation uses strongly consistent reads; otherwise, eventually
            consistent reads are used.

        :type return_consumed_capacity: string
        :param return_consumed_capacity: A value that if set to `TOTAL`, the
            response includes ConsumedCapacity data for tables and indexes. If
            set to `INDEXES`, the response includes ConsumedCapacity for
            indexes. If set to `NONE` (the default), ConsumedCapacity is not
            included in the response.

        :type projection_expression: string
        :param projection_expression: A string that identifies one or more
            attributes to retrieve from the table. These attributes can include
            scalars, sets, or elements of a JSON document. The attributes in
            the expression must be separated by commas.
        If no attribute names are specified, then all attributes will be
            returned. If any of the requested attributes are not found, they
            will not appear in the result.

        For more information on projection expressions, go to `Accessing Item
            Attributes`_ in the Amazon DynamoDB Developer Guide .

        :type expression_attribute_names: map
        :param expression_attribute_names: One or more substitution tokens for
            simplifying complex expressions. The following are some use cases
            for using ExpressionAttributeNames :

        + To shorten an attribute name that is very long or unwieldy in an
              expression.
        + To create a placeholder for repeating occurrences of an attribute
              name in an expression.
        + To prevent special characters in an attribute name from being
              misinterpreted in an expression.


        Use the **#** character in an expression to dereference an attribute
            name. For example, consider the following expression:


        + `order.customerInfo.LastName = "Smith" OR order.customerInfo.LastName
              = "Jones"`


        Now suppose that you specified the following for
            ExpressionAttributeNames :


        + `{"#name":"order.customerInfo.LastName"}`


        The expression can now be simplified as follows:


        + `#name = "Smith" OR #name = "Jones"`


        For more information on expression attribute names, go to `Accessing
            Item Attributes`_ in the Amazon DynamoDB Developer Guide .

        """
        params = {'TableName': table_name, 'Key': key, }
        if attributes_to_get is not None:
            params['AttributesToGet'] = attributes_to_get
        if consistent_read is not None:
            params['ConsistentRead'] = consistent_read
        if return_consumed_capacity is not None:
            params['ReturnConsumedCapacity'] = return_consumed_capacity
        if projection_expression is not None:
            params['ProjectionExpression'] = projection_expression
        if expression_attribute_names is not None:
            params['ExpressionAttributeNames'] = expression_attribute_names
        return self.make_request(action='GetItem',
                                 body=json.dumps(params))

    def list_tables(self, exclusive_start_table_name=None, limit=None):
        """
        Returns an array of table names associated with the current
        account and endpoint. The output from ListTables is paginated,
        with each page returning a maximum of 100 table names.

        :type exclusive_start_table_name: string
        :param exclusive_start_table_name: The first table name that this
            operation will evaluate. Use the value that was returned for
            LastEvaluatedTableName in a previous operation, so that you can
            obtain the next page of results.

        :type limit: integer
        :param limit: A maximum number of table names to return. If this
            parameter is not specified, the limit is 100.

        """
        params = {}
        if exclusive_start_table_name is not None:
            params['ExclusiveStartTableName'] = exclusive_start_table_name
        if limit is not None:
            params['Limit'] = limit
        return self.make_request(action='ListTables',
                                 body=json.dumps(params))

    def put_item(self, table_name, item, expected=None, return_values=None,
                 return_consumed_capacity=None,
                 return_item_collection_metrics=None,
                 conditional_operator=None, condition_expression=None,
                 expression_attribute_names=None,
                 expression_attribute_values=None):
        """
        Creates a new item, or replaces an old item with a new item.
        If an item that has the same primary key as the new item
        already exists in the specified table, the new item completely
        replaces the existing item. You can perform a conditional put
        operation (add a new item if one with the specified primary
        key doesn't exist), or replace an existing item if it has
        certain attribute values.

        In addition to putting an item, you can also return the item's
        attribute values in the same operation, using the ReturnValues
        parameter.

        When you add an item, the primary key attribute(s) are the
        only required attributes. Attribute values cannot be null.
        String and Binary type attributes must have lengths greater
        than zero. Set type attributes cannot be empty. Requests with
        empty values will be rejected with a ValidationException
        exception.

        You can request that PutItem return either a copy of the
        original item (before the update) or a copy of the updated
        item (after the update). For more information, see the
        ReturnValues description below.


        To prevent a new item from replacing an existing item, use a
        conditional put operation with ComparisonOperator set to
        `NULL` for the primary key attribute, or attributes.


        For more information about using this API, see `Working with
        Items`_ in the Amazon DynamoDB Developer Guide .

        :type table_name: string
        :param table_name: The name of the table to contain the item.

        :type item: map
        :param item: A map of attribute name/value pairs, one for each
            attribute. Only the primary key attributes are required; you can
            optionally provide other attribute name-value pairs for the item.
        You must provide all of the attributes for the primary key. For
            example, with a hash type primary key, you only need to specify the
            hash attribute. For a hash-and-range type primary key, you must
            specify both the hash attribute and the range attribute.

        If you specify any attributes that are part of an index key, then the
            data types for those attributes must match those of the schema in
            the table's attribute definition.

        For more information about primary keys, see `Primary Key`_ in the
            Amazon DynamoDB Developer Guide .

        Each element in the Item map is an AttributeValue object.

        :type expected: map
        :param expected:
        There is a newer parameter available. Use ConditionExpression instead.
            Note that if you use Expected and ConditionExpression at the same
            time, DynamoDB will return a ValidationException exception.

        This parameter does not support lists or maps.

        A map of attribute/condition pairs. Expected provides a conditional
            block for the PutItem operation.

        Each element of Expected consists of an attribute name, a comparison
            operator, and one or more values. DynamoDB compares the attribute
            with the value(s) you supplied, using the comparison operator. For
            each Expected element, the result of the evaluation is either true
            or false.

        If you specify more than one element in the Expected map, then by
            default all of the conditions must evaluate to true. In other
            words, the conditions are ANDed together. (You can use the
            ConditionalOperator parameter to OR the conditions instead. If you
            do this, then at least one of the conditions must evaluate to true,
            rather than all of them.)

        If the Expected map evaluates to true, then the conditional operation
            succeeds; otherwise, it fails.

        Expected contains the following:


        + AttributeValueList - One or more values to evaluate against the
              supplied attribute. The number of values in the list depends on the
              ComparisonOperator being used. For type Number, value comparisons
              are numeric. String value comparisons for greater than, equals, or
              less than are based on ASCII character code values. For example,
              `a` is greater than `A`, and `a` is greater than `B`. For a list of
              code values, see
              `http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters`_.
              For type Binary, DynamoDB treats each byte of the binary data as
              unsigned when it compares binary values, for example when
              evaluating query expressions.
        + ComparisonOperator - A comparator for evaluating attributes in the
              AttributeValueList . When performing the comparison, DynamoDB uses
              strongly consistent reads. The following comparison operators are
              available: `EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL |
              CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN` The following
              are descriptions of each comparison operator.

            + `EQ` : Equal. `EQ` is supported for all datatypes, including lists
                and maps. AttributeValueList can contain only one AttributeValue
                element of type String, Number, Binary, String Set, Number Set, or
                Binary Set. If an item contains an AttributeValue element of a
                different type than the one specified in the request, the value
                does not match. For example, `{"S":"6"}` does not equal
                `{"N":"6"}`. Also, `{"N":"6"}` does not equal `{"NS":["6", "2",
                "1"]}`. > <li>
            + `NE` : Not equal. `NE` is supported for all datatypes, including
                lists and maps. AttributeValueList can contain only one
                AttributeValue of type String, Number, Binary, String Set, Number
                Set, or Binary Set. If an item contains an AttributeValue of a
                different type than the one specified in the request, the value
                does not match. For example, `{"S":"6"}` does not equal
                `{"N":"6"}`. Also, `{"N":"6"}` does not equal `{"NS":["6", "2",
                "1"]}`. > <li>
            + `LE` : Less than or equal. AttributeValueList can contain only one
                AttributeValue element of type String, Number, or Binary (not a set
                type). If an item contains an AttributeValue element of a different
                type than the one specified in the request, the value does not
                match. For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `LT` : Less than. AttributeValueList can contain only one
                AttributeValue of type String, Number, or Binary (not a set type).
                If an item contains an AttributeValue element of a different type
                than the one specified in the request, the value does not match.
                For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `GE` : Greater than or equal. AttributeValueList can contain only one
                AttributeValue element of type String, Number, or Binary (not a set
                type). If an item contains an AttributeValue element of a different
                type than the one specified in the request, the value does not
                match. For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `GT` : Greater than. AttributeValueList can contain only one
                AttributeValue element of type String, Number, or Binary (not a set
                type). If an item contains an AttributeValue element of a different
                type than the one specified in the request, the value does not
                match. For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `NOT_NULL` : The attribute exists. `NOT_NULL` is supported for all
                  datatypes, including lists and maps. This operator tests for the
                  existence of an attribute, not its data type. If the data type of
                  attribute " `a`" is null, and you evaluate it using `NOT_NULL`, the
                  result is a Boolean true . This result is because the attribute "
                  `a`" exists; its data type is not relevant to the `NOT_NULL`
                  comparison operator.
            + `NULL` : The attribute does not exist. `NULL` is supported for all
                  datatypes, including lists and maps. This operator tests for the
                  nonexistence of an attribute, not its data type. If the data type
                  of attribute " `a`" is null, and you evaluate it using `NULL`, the
                  result is a Boolean false . This is because the attribute " `a`"
                  exists; its data type is not relevant to the `NULL` comparison
                  operator.
            + `CONTAINS` : Checks for a subsequence, or value in a set.
                  AttributeValueList can contain only one AttributeValue element of
                  type String, Number, or Binary (not a set type). If the target
                  attribute of the comparison is of type String, then the operator
                  checks for a substring match. If the target attribute of the
                  comparison is of type Binary, then the operator looks for a
                  subsequence of the target that matches the input. If the target
                  attribute of the comparison is a set (" `SS`", " `NS`", or "
                  `BS`"), then the operator evaluates to true if it finds an exact
                  match with any member of the set. CONTAINS is supported for lists:
                  When evaluating " `a CONTAINS b`", " `a`" can be a list; however, "
                  `b`" cannot be a set, a map, or a list.
            + `NOT_CONTAINS` : Checks for absence of a subsequence, or absence of a
                  value in a set. AttributeValueList can contain only one
                  AttributeValue element of type String, Number, or Binary (not a set
                  type). If the target attribute of the comparison is a String, then
                  the operator checks for the absence of a substring match. If the
                  target attribute of the comparison is Binary, then the operator
                  checks for the absence of a subsequence of the target that matches
                  the input. If the target attribute of the comparison is a set ("
                  `SS`", " `NS`", or " `BS`"), then the operator evaluates to true if
                  it does not find an exact match with any member of the set.
                  NOT_CONTAINS is supported for lists: When evaluating " `a NOT
                  CONTAINS b`", " `a`" can be a list; however, " `b`" cannot be a
                  set, a map, or a list.
            + `BEGINS_WITH` : Checks for a prefix. AttributeValueList can contain
                only one AttributeValue of type String or Binary (not a Number or a
                set type). The target attribute of the comparison must be of type
                String or Binary (not a Number or a set type). > <li>
            + `IN` : Checks for matching elements within two sets.
                  AttributeValueList can contain one or more AttributeValue elements
                  of type String, Number, or Binary (not a set type). These
                  attributes are compared against an existing set type attribute of
                  an item. If any elements of the input set are present in the item
                  attribute, the expression evaluates to true.
            + `BETWEEN` : Greater than or equal to the first value, and less than
                  or equal to the second value. AttributeValueList must contain two
                  AttributeValue elements of the same type, either String, Number, or
                  Binary (not a set type). A target attribute matches if the target
                  value is greater than, or equal to, the first element and less
                  than, or equal to, the second element. If an item contains an
                  AttributeValue element of a different type than the one specified
                  in the request, the value does not match. For example, `{"S":"6"}`
                  does not compare to `{"N":"6"}`. Also, `{"N":"6"}` does not compare
                  to `{"NS":["6", "2", "1"]}`



        For usage examples of AttributeValueList and ComparisonOperator , see
            `Legacy Conditional Parameters`_ in the Amazon DynamoDB Developer
            Guide .

        For backward compatibility with previous DynamoDB releases, the
            following parameters can be used instead of AttributeValueList and
            ComparisonOperator :


        + Value - A value for DynamoDB to compare with an attribute.
        + Exists - A Boolean value that causes DynamoDB to evaluate the value
              before attempting the conditional operation:

            + If Exists is `True`, DynamoDB will check to see if that attribute
                  value already exists in the table. If it is found, then the
                  condition evaluates to true; otherwise the condition evaluate to
                  false.
            + If Exists is `False`, DynamoDB assumes that the attribute value does
                  not exist in the table. If in fact the value does not exist, then
                  the assumption is valid and the condition evaluates to true. If the
                  value is found, despite the assumption that it does not exist, the
                  condition evaluates to false.
          Note that the default value for Exists is `True`.


        The Value and Exists parameters are incompatible with
            AttributeValueList and ComparisonOperator . Note that if you use
            both sets of parameters at once, DynamoDB will return a
            ValidationException exception.

        :type return_values: string
        :param return_values:
        Use ReturnValues if you want to get the item attributes as they
            appeared before they were updated with the PutItem request. For
            PutItem , the valid values are:


        + `NONE` - If ReturnValues is not specified, or if its value is `NONE`,
              then nothing is returned. (This setting is the default for
              ReturnValues .)
        + `ALL_OLD` - If PutItem overwrote an attribute name-value pair, then
              the content of the old item is returned.

        :type return_consumed_capacity: string
        :param return_consumed_capacity: A value that if set to `TOTAL`, the
            response includes ConsumedCapacity data for tables and indexes. If
            set to `INDEXES`, the response includes ConsumedCapacity for
            indexes. If set to `NONE` (the default), ConsumedCapacity is not
            included in the response.

        :type return_item_collection_metrics: string
        :param return_item_collection_metrics: A value that if set to `SIZE`,
            the response includes statistics about item collections, if any,
            that were modified during the operation are returned in the
            response. If set to `NONE` (the default), no statistics are
            returned.

        :type conditional_operator: string
        :param conditional_operator:
        There is a newer parameter available. Use ConditionExpression instead.
            Note that if you use ConditionalOperator and ConditionExpression at
            the same time, DynamoDB will return a ValidationException
            exception.

        This parameter does not support lists or maps.

        A logical operator to apply to the conditions in the Expected map:


        + `AND` - If all of the conditions evaluate to true, then the entire
              map evaluates to true.
        + `OR` - If at least one of the conditions evaluate to true, then the
              entire map evaluates to true.


        If you omit ConditionalOperator , then `AND` is the default.

        The operation will succeed only if the entire map evaluates to true.

        :type condition_expression: string
        :param condition_expression: A condition that must be satisfied in
            order for a conditional PutItem operation to succeed.
        An expression can contain any of the following:


        + Boolean functions: `attribute_exists | attribute_not_exists |
              contains | begins_with` These function names are case-sensitive.
        + Comparison operators: ` = | <> | < | > | <=
              | >= | BETWEEN | IN`
        + Logical operators: `AND | OR | NOT`


        For more information on condition expressions, go to `Specifying
            Conditions`_ in the Amazon DynamoDB Developer Guide .

        :type expression_attribute_names: map
        :param expression_attribute_names: One or more substitution tokens for
            simplifying complex expressions. The following are some use cases
            for using ExpressionAttributeNames :

        + To shorten an attribute name that is very long or unwieldy in an
              expression.
        + To create a placeholder for repeating occurrences of an attribute
              name in an expression.
        + To prevent special characters in an attribute name from being
              misinterpreted in an expression.


        Use the **#** character in an expression to dereference an attribute
            name. For example, consider the following expression:


        + `order.customerInfo.LastName = "Smith" OR order.customerInfo.LastName
              = "Jones"`


        Now suppose that you specified the following for
            ExpressionAttributeNames :


        + `{"#name":"order.customerInfo.LastName"}`


        The expression can now be simplified as follows:


        + `#name = "Smith" OR #name = "Jones"`


        For more information on expression attribute names, go to `Accessing
            Item Attributes`_ in the Amazon DynamoDB Developer Guide .

        :type expression_attribute_values: map
        :param expression_attribute_values: One or more values that can be
            substituted in an expression.
        Use the **:** (colon) character in an expression to dereference an
            attribute value. For example, suppose that you wanted to check
            whether the value of the ProductStatus attribute was one of the
            following:

        `Available | Backordered | Discontinued`

        You would first need to specify ExpressionAttributeValues as follows:

        `{ ":avail":{"S":"Available"}, ":back":{"S":"Backordered"},
            ":disc":{"S":"Discontinued"} }`

        You could then use these values in an expression, such as this:

        `ProductStatus IN (:avail, :back, :disc)`

        For more information on expression attribute values, go to `Specifying
            Conditions`_ in the Amazon DynamoDB Developer Guide .

        """
        params = {'TableName': table_name, 'Item': item, }
        if expected is not None:
            params['Expected'] = expected
        if return_values is not None:
            params['ReturnValues'] = return_values
        if return_consumed_capacity is not None:
            params['ReturnConsumedCapacity'] = return_consumed_capacity
        if return_item_collection_metrics is not None:
            params['ReturnItemCollectionMetrics'] = return_item_collection_metrics
        if conditional_operator is not None:
            params['ConditionalOperator'] = conditional_operator
        if condition_expression is not None:
            params['ConditionExpression'] = condition_expression
        if expression_attribute_names is not None:
            params['ExpressionAttributeNames'] = expression_attribute_names
        if expression_attribute_values is not None:
            params['ExpressionAttributeValues'] = expression_attribute_values
        return self.make_request(action='PutItem',
                                 body=json.dumps(params))

    def query(self, table_name, key_conditions, index_name=None, select=None,
              attributes_to_get=None, limit=None, consistent_read=None,
              query_filter=None, conditional_operator=None,
              scan_index_forward=None, exclusive_start_key=None,
              return_consumed_capacity=None, projection_expression=None,
              filter_expression=None, expression_attribute_names=None,
              expression_attribute_values=None):
        """
        A Query operation directly accesses items from a table using
        the table primary key, or from an index using the index key.
        You must provide a specific hash key value. You can narrow the
        scope of the query by using comparison operators on the range
        key value, or on the index key. You can use the
        ScanIndexForward parameter to get results in forward or
        reverse order, by range key or by index key.

        Queries that do not return results consume the minimum number
        of read capacity units for that type of read operation.

        If the total number of items meeting the query criteria
        exceeds the result set size limit of 1 MB, the query stops and
        results are returned to the user with LastEvaluatedKey to
        continue the query in a subsequent operation. Unlike a Scan
        operation, a Query operation never returns both an empty
        result set and a LastEvaluatedKey . The LastEvaluatedKey is
        only provided if the results exceed 1 MB, or if you have used
        Limit .

        You can query a table, a local secondary index, or a global
        secondary index. For a query on a table or on a local
        secondary index, you can set ConsistentRead to true and obtain
        a strongly consistent result. Global secondary indexes support
        eventually consistent reads only, so do not specify
        ConsistentRead when querying a global secondary index.

        :type table_name: string
        :param table_name: The name of the table containing the requested
            items.

        :type index_name: string
        :param index_name: The name of an index to query. This index can be any
            local secondary index or global secondary index on the table.

        :type select: string
        :param select: The attributes to be returned in the result. You can
            retrieve all item attributes, specific item attributes, the count
            of matching items, or in the case of an index, some or all of the
            attributes projected into the index.

        + `ALL_ATTRIBUTES` - Returns all of the item attributes from the
              specified table or index. If you query a local secondary index,
              then for each matching item in the index DynamoDB will fetch the
              entire item from the parent table. If the index is configured to
              project all item attributes, then all of the data can be obtained
              from the local secondary index, and no fetching is required.
        + `ALL_PROJECTED_ATTRIBUTES` - Allowed only when querying an index.
              Retrieves all attributes that have been projected into the index.
              If the index is configured to project all attributes, this return
              value is equivalent to specifying `ALL_ATTRIBUTES`.
        + `COUNT` - Returns the number of matching items, rather than the
              matching items themselves.
        + `SPECIFIC_ATTRIBUTES` - Returns only the attributes listed in
              AttributesToGet . This return value is equivalent to specifying
              AttributesToGet without specifying any value for Select . If you
              query a local secondary index and request only attributes that are
              projected into that index, the operation will read only the index
              and not the table. If any of the requested attributes are not
              projected into the local secondary index, DynamoDB will fetch each
              of these attributes from the parent table. This extra fetching
              incurs additional throughput cost and latency. If you query a
              global secondary index, you can only request attributes that are
              projected into the index. Global secondary index queries cannot
              fetch attributes from the parent table.


        If neither Select nor AttributesToGet are specified, DynamoDB defaults
            to `ALL_ATTRIBUTES` when accessing a table, and
            `ALL_PROJECTED_ATTRIBUTES` when accessing an index. You cannot use
            both Select and AttributesToGet together in a single request,
            unless the value for Select is `SPECIFIC_ATTRIBUTES`. (This usage
            is equivalent to specifying AttributesToGet without any value for
            Select .)

        :type attributes_to_get: list
        :param attributes_to_get:
        There is a newer parameter available. Use ProjectionExpression instead.
            Note that if you use AttributesToGet and ProjectionExpression at
            the same time, DynamoDB will return a ValidationException
            exception.

        This parameter allows you to retrieve lists or maps; however, it cannot
            retrieve individual list or map elements.

        The names of one or more attributes to retrieve. If no attribute names
            are specified, then all attributes will be returned. If any of the
            requested attributes are not found, they will not appear in the
            result.

        Note that AttributesToGet has no effect on provisioned throughput
            consumption. DynamoDB determines capacity units consumed based on
            item size, not on the amount of data that is returned to an
            application.

        You cannot use both AttributesToGet and Select together in a Query
            request, unless the value for Select is `SPECIFIC_ATTRIBUTES`.
            (This usage is equivalent to specifying AttributesToGet without any
            value for Select .)

        If you query a local secondary index and request only attributes that
            are projected into that index, the operation will read only the
            index and not the table. If any of the requested attributes are not
            projected into the local secondary index, DynamoDB will fetch each
            of these attributes from the parent table. This extra fetching
            incurs additional throughput cost and latency.

        If you query a global secondary index, you can only request attributes
            that are projected into the index. Global secondary index queries
            cannot fetch attributes from the parent table.

        :type limit: integer
        :param limit: The maximum number of items to evaluate (not necessarily
            the number of matching items). If DynamoDB processes the number of
            items up to the limit while processing the results, it stops the
            operation and returns the matching values up to that point, and a
            key in LastEvaluatedKey to apply in a subsequent operation, so that
            you can pick up where you left off. Also, if the processed data set
            size exceeds 1 MB before DynamoDB reaches this limit, it stops the
            operation and returns the matching values up to the limit, and a
            key in LastEvaluatedKey to apply in a subsequent operation to
            continue the operation. For more information, see `Query and Scan`_
            in the Amazon DynamoDB Developer Guide .

        :type consistent_read: boolean
        :param consistent_read: A value that if set to `True`, then the
            operation uses strongly consistent reads; otherwise, eventually
            consistent reads are used.
        Strongly consistent reads are not supported on global secondary
            indexes. If you query a global secondary index with ConsistentRead
            set to `True`, you will receive an error message.

        :type key_conditions: map
        :param key_conditions: The selection criteria for the query. For a
            query on a table, you can have conditions only on the table primary
            key attributes. You must specify the hash key attribute name and
            value as an `EQ` condition. You can optionally specify a second
            condition, referring to the range key attribute. If you do not
            specify a range key condition, all items under the hash key will be
            fetched and processed. Any filters will applied after this.
        For a query on an index, you can have conditions only on the index key
            attributes. You must specify the index hash attribute name and
            value as an EQ condition. You can optionally specify a second
            condition, referring to the index key range attribute.

        Each KeyConditions element consists of an attribute name to compare,
            along with the following:


        + AttributeValueList - One or more values to evaluate against the
              supplied attribute. The number of values in the list depends on the
              ComparisonOperator being used. For type Number, value comparisons
              are numeric. String value comparisons for greater than, equals, or
              less than are based on ASCII character code values. For example,
              `a` is greater than `A`, and `a` is greater than `B`. For a list of
              code values, see
              `http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters`_.
              For Binary, DynamoDB treats each byte of the binary data as
              unsigned when it compares binary values, for example when
              evaluating query expressions.
        + ComparisonOperator - A comparator for evaluating attributes, for
              example, equals, greater than, less than, and so on. For
              KeyConditions , only the following comparison operators are
              supported: `EQ | LE | LT | GE | GT | BEGINS_WITH | BETWEEN` The
              following are descriptions of these comparison operators.

            + `EQ` : Equal. AttributeValueList can contain only one AttributeValue
                  of type String, Number, or Binary (not a set type). If an item
                  contains an AttributeValue element of a different type than the one
                  specified in the request, the value does not match. For example,
                  `{"S":"6"}` does not equal `{"N":"6"}`. Also, `{"N":"6"}` does not
                  equal `{"NS":["6", "2", "1"]}`.
            + `LE` : Less than or equal. AttributeValueList can contain only one
                AttributeValue element of type String, Number, or Binary (not a set
                type). If an item contains an AttributeValue element of a different
                type than the one specified in the request, the value does not
                match. For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `LT` : Less than. AttributeValueList can contain only one
                AttributeValue of type String, Number, or Binary (not a set type).
                If an item contains an AttributeValue element of a different type
                than the one specified in the request, the value does not match.
                For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `GE` : Greater than or equal. AttributeValueList can contain only one
                AttributeValue element of type String, Number, or Binary (not a set
                type). If an item contains an AttributeValue element of a different
                type than the one specified in the request, the value does not
                match. For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `GT` : Greater than. AttributeValueList can contain only one
                AttributeValue element of type String, Number, or Binary (not a set
                type). If an item contains an AttributeValue element of a different
                type than the one specified in the request, the value does not
                match. For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `BEGINS_WITH` : Checks for a prefix. AttributeValueList can contain
                only one AttributeValue of type String or Binary (not a Number or a
                set type). The target attribute of the comparison must be of type
                String or Binary (not a Number or a set type). > <li>
            + `BETWEEN` : Greater than or equal to the first value, and less than
                  or equal to the second value. AttributeValueList must contain two
                  AttributeValue elements of the same type, either String, Number, or
                  Binary (not a set type). A target attribute matches if the target
                  value is greater than, or equal to, the first element and less
                  than, or equal to, the second element. If an item contains an
                  AttributeValue element of a different type than the one specified
                  in the request, the value does not match. For example, `{"S":"6"}`
                  does not compare to `{"N":"6"}`. Also, `{"N":"6"}` does not compare
                  to `{"NS":["6", "2", "1"]}`



        For usage examples of AttributeValueList and ComparisonOperator , see
            `Legacy Conditional Parameters`_ in the Amazon DynamoDB Developer
            Guide .

        :type query_filter: map
        :param query_filter:
        There is a newer parameter available. Use FilterExpression instead.
            Note that if you use QueryFilter and FilterExpression at the same
            time, DynamoDB will return a ValidationException exception.

        This parameter does not support lists or maps.

        A condition that evaluates the query results after the items are read
            and returns only the desired values.
        Query filters are applied after the items are read, so they do not
            limit the capacity used.
        If you specify more than one condition in the QueryFilter map, then by
            default all of the conditions must evaluate to true. In other
            words, the conditions are ANDed together. (You can use the
            ConditionalOperator parameter to OR the conditions instead. If you
            do this, then at least one of the conditions must evaluate to true,
            rather than all of them.)


        QueryFilter does not allow key attributes. You cannot define a filter
            condition on a hash key or range key.


        Each QueryFilter element consists of an attribute name to compare,
            along with the following:


        + AttributeValueList - One or more values to evaluate against the
              supplied attribute. The number of values in the list depends on the
              operator specified in ComparisonOperator . For type Number, value
              comparisons are numeric. String value comparisons for greater than,
              equals, or less than are based on ASCII character code values. For
              example, `a` is greater than `A`, and `a` is greater than `B`. For
              a list of code values, see
              `http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters`_.
              For type Binary, DynamoDB treats each byte of the binary data as
              unsigned when it compares binary values, for example when
              evaluating query expressions. For information on specifying data
              types in JSON, see `JSON Data Format`_ in the Amazon DynamoDB
              Developer Guide .
        + ComparisonOperator - A comparator for evaluating attributes. For
              example, equals, greater than, less than, etc. The following
              comparison operators are available: `EQ | NE | LE | LT | GE | GT |
              NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN |
              BETWEEN` For complete descriptions of all comparison operators, see
              `API_Condition.html`_.

        :type conditional_operator: string
        :param conditional_operator:
        This parameter does not support lists or maps.

        A logical operator to apply to the conditions in the QueryFilter map:


        + `AND` - If all of the conditions evaluate to true, then the entire
              map evaluates to true.
        + `OR` - If at least one of the conditions evaluate to true, then the
              entire map evaluates to true.


        If you omit ConditionalOperator , then `AND` is the default.

        The operation will succeed only if the entire map evaluates to true.

        :type scan_index_forward: boolean
        :param scan_index_forward: A value that specifies ascending (true) or
            descending (false) traversal of the index. DynamoDB returns results
            reflecting the requested order determined by the range key. If the
            data type is Number, the results are returned in numeric order. For
            type String, the results are returned in order of ASCII character
            code values. For type Binary, DynamoDB treats each byte of the
            binary data as unsigned when it compares binary values.
        If ScanIndexForward is not specified, the results are returned in
            ascending order.

        :type exclusive_start_key: map
        :param exclusive_start_key: The primary key of the first item that this
            operation will evaluate. Use the value that was returned for
            LastEvaluatedKey in the previous operation.
        The data type for ExclusiveStartKey must be String, Number or Binary.
            No set data types are allowed.

        :type return_consumed_capacity: string
        :param return_consumed_capacity: A value that if set to `TOTAL`, the
            response includes ConsumedCapacity data for tables and indexes. If
            set to `INDEXES`, the response includes ConsumedCapacity for
            indexes. If set to `NONE` (the default), ConsumedCapacity is not
            included in the response.

        :type projection_expression: string
        :param projection_expression: A string that identifies one or more
            attributes to retrieve from the table. These attributes can include
            scalars, sets, or elements of a JSON document. The attributes in
            the expression must be separated by commas.
        If no attribute names are specified, then all attributes will be
            returned. If any of the requested attributes are not found, they
            will not appear in the result.

        For more information on projection expressions, go to `Accessing Item
            Attributes`_ in the Amazon DynamoDB Developer Guide .

        :type filter_expression: string
        :param filter_expression: A condition that evaluates the query results
            after the items are read and returns only the desired values.
        The condition you specify is applied to the items queried; any items
            that do not match the expression are not returned.
        Filter expressions are applied after the items are read, so they do not
            limit the capacity used.
        A FilterExpression has the same syntax as a ConditionExpression . For
            more information on expression syntax, go to `Specifying
            Conditions`_ in the Amazon DynamoDB Developer Guide .

        :type expression_attribute_names: map
        :param expression_attribute_names: One or more substitution tokens for
            simplifying complex expressions. The following are some use cases
            for using ExpressionAttributeNames :

        + To shorten an attribute name that is very long or unwieldy in an
              expression.
        + To create a placeholder for repeating occurrences of an attribute
              name in an expression.
        + To prevent special characters in an attribute name from being
              misinterpreted in an expression.


        Use the **#** character in an expression to dereference an attribute
            name. For example, consider the following expression:


        + `order.customerInfo.LastName = "Smith" OR order.customerInfo.LastName
              = "Jones"`


        Now suppose that you specified the following for
            ExpressionAttributeNames :


        + `{"#name":"order.customerInfo.LastName"}`


        The expression can now be simplified as follows:


        + `#name = "Smith" OR #name = "Jones"`


        For more information on expression attribute names, go to `Accessing
            Item Attributes`_ in the Amazon DynamoDB Developer Guide .

        :type expression_attribute_values: map
        :param expression_attribute_values: One or more values that can be
            substituted in an expression.
        Use the **:** (colon) character in an expression to dereference an
            attribute value. For example, suppose that you wanted to check
            whether the value of the ProductStatus attribute was one of the
            following:

        `Available | Backordered | Discontinued`

        You would first need to specify ExpressionAttributeValues as follows:

        `{ ":avail":{"S":"Available"}, ":back":{"S":"Backordered"},
            ":disc":{"S":"Discontinued"} }`

        You could then use these values in an expression, such as this:

        `ProductStatus IN (:avail, :back, :disc)`

        For more information on expression attribute values, go to `Specifying
            Conditions`_ in the Amazon DynamoDB Developer Guide .

        """
        params = {
            'TableName': table_name,
            'KeyConditions': key_conditions,
        }
        if index_name is not None:
            params['IndexName'] = index_name
        if select is not None:
            params['Select'] = select
        if attributes_to_get is not None:
            params['AttributesToGet'] = attributes_to_get
        if limit is not None:
            params['Limit'] = limit
        if consistent_read is not None:
            params['ConsistentRead'] = consistent_read
        if query_filter is not None:
            params['QueryFilter'] = query_filter
        if conditional_operator is not None:
            params['ConditionalOperator'] = conditional_operator
        if scan_index_forward is not None:
            params['ScanIndexForward'] = scan_index_forward
        if exclusive_start_key is not None:
            params['ExclusiveStartKey'] = exclusive_start_key
        if return_consumed_capacity is not None:
            params['ReturnConsumedCapacity'] = return_consumed_capacity
        if projection_expression is not None:
            params['ProjectionExpression'] = projection_expression
        if filter_expression is not None:
            params['FilterExpression'] = filter_expression
        if expression_attribute_names is not None:
            params['ExpressionAttributeNames'] = expression_attribute_names
        if expression_attribute_values is not None:
            params['ExpressionAttributeValues'] = expression_attribute_values
        return self.make_request(action='Query',
                                 body=json.dumps(params))

    def scan(self, table_name, attributes_to_get=None, limit=None,
             select=None, scan_filter=None, conditional_operator=None,
             exclusive_start_key=None, return_consumed_capacity=None,
             total_segments=None, segment=None, projection_expression=None,
             filter_expression=None, expression_attribute_names=None,
             expression_attribute_values=None):
        """
        The Scan operation returns one or more items and item
        attributes by accessing every item in the table. To have
        DynamoDB return fewer items, you can provide a ScanFilter
        operation.

        If the total number of scanned items exceeds the maximum data
        set size limit of 1 MB, the scan stops and results are
        returned to the user as a LastEvaluatedKey value to continue
        the scan in a subsequent operation. The results also include
        the number of items exceeding the limit. A scan can result in
        no table data meeting the filter criteria.

        The result set is eventually consistent.

        By default, Scan operations proceed sequentially; however, for
        faster performance on large tables, applications can request a
        parallel Scan operation by specifying the Segment and
        TotalSegments parameters. For more information, see `Parallel
        Scan`_ in the Amazon DynamoDB Developer Guide .

        :type table_name: string
        :param table_name: The name of the table containing the requested
            items.

        :type attributes_to_get: list
        :param attributes_to_get:
        There is a newer parameter available. Use ProjectionExpression instead.
            Note that if you use AttributesToGet and ProjectionExpression at
            the same time, DynamoDB will return a ValidationException
            exception.

        This parameter allows you to retrieve lists or maps; however, it cannot
            retrieve individual list or map elements.

        The names of one or more attributes to retrieve. If no attribute names
            are specified, then all attributes will be returned. If any of the
            requested attributes are not found, they will not appear in the
            result.

        Note that AttributesToGet has no effect on provisioned throughput
            consumption. DynamoDB determines capacity units consumed based on
            item size, not on the amount of data that is returned to an
            application.

        :type limit: integer
        :param limit: The maximum number of items to evaluate (not necessarily
            the number of matching items). If DynamoDB processes the number of
            items up to the limit while processing the results, it stops the
            operation and returns the matching values up to that point, and a
            key in LastEvaluatedKey to apply in a subsequent operation, so that
            you can pick up where you left off. Also, if the processed data set
            size exceeds 1 MB before DynamoDB reaches this limit, it stops the
            operation and returns the matching values up to the limit, and a
            key in LastEvaluatedKey to apply in a subsequent operation to
            continue the operation. For more information, see `Query and Scan`_
            in the Amazon DynamoDB Developer Guide .

        :type select: string
        :param select: The attributes to be returned in the result. You can
            retrieve all item attributes, specific item attributes, or the
            count of matching items.

        + `ALL_ATTRIBUTES` - Returns all of the item attributes.
        + `COUNT` - Returns the number of matching items, rather than the
              matching items themselves.
        + `SPECIFIC_ATTRIBUTES` - Returns only the attributes listed in
              AttributesToGet . This return value is equivalent to specifying
              AttributesToGet without specifying any value for Select .


        If neither Select nor AttributesToGet are specified, DynamoDB defaults
            to `ALL_ATTRIBUTES`. You cannot use both AttributesToGet and Select
            together in a single request, unless the value for Select is
            `SPECIFIC_ATTRIBUTES`. (This usage is equivalent to specifying
            AttributesToGet without any value for Select .)

        :type scan_filter: map
        :param scan_filter:
        There is a newer parameter available. Use FilterExpression instead.
            Note that if you use ScanFilter and FilterExpression at the same
            time, DynamoDB will return a ValidationException exception.

        This parameter does not support lists or maps.

        A condition that evaluates the scan results and returns only the
            desired values.

        If you specify more than one condition in the ScanFilter map, then by
            default all of the conditions must evaluate to true. In other
            words, the conditions are ANDed together. (You can use the
            ConditionalOperator parameter to OR the conditions instead. If you
            do this, then at least one of the conditions must evaluate to true,
            rather than all of them.)

        Each ScanFilter element consists of an attribute name to compare, along
            with the following:


        + AttributeValueList - One or more values to evaluate against the
              supplied attribute. The number of values in the list depends on the
              operator specified in ComparisonOperator . For type Number, value
              comparisons are numeric. String value comparisons for greater than,
              equals, or less than are based on ASCII character code values. For
              example, `a` is greater than `A`, and `a` is greater than `B`. For
              a list of code values, see
              `http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters`_.
              For Binary, DynamoDB treats each byte of the binary data as
              unsigned when it compares binary values, for example when
              evaluating query expressions. For information on specifying data
              types in JSON, see `JSON Data Format`_ in the Amazon DynamoDB
              Developer Guide .
        + ComparisonOperator - A comparator for evaluating attributes. For
              example, equals, greater than, less than, etc. The following
              comparison operators are available: `EQ | NE | LE | LT | GE | GT |
              NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN |
              BETWEEN` For complete descriptions of all comparison operators, see
              `Condition`_.

        :type conditional_operator: string
        :param conditional_operator:
        There is a newer parameter available. Use ConditionExpression instead.
            Note that if you use ConditionalOperator and ConditionExpression at
            the same time, DynamoDB will return a ValidationException
            exception.

        This parameter does not support lists or maps.

        A logical operator to apply to the conditions in the ScanFilter map:


        + `AND` - If all of the conditions evaluate to true, then the entire
              map evaluates to true.
        + `OR` - If at least one of the conditions evaluate to true, then the
              entire map evaluates to true.


        If you omit ConditionalOperator , then `AND` is the default.

        The operation will succeed only if the entire map evaluates to true.

        :type exclusive_start_key: map
        :param exclusive_start_key: The primary key of the first item that this
            operation will evaluate. Use the value that was returned for
            LastEvaluatedKey in the previous operation.
        The data type for ExclusiveStartKey must be String, Number or Binary.
            No set data types are allowed.

        In a parallel scan, a Scan request that includes ExclusiveStartKey must
            specify the same segment whose previous Scan returned the
            corresponding value of LastEvaluatedKey .

        :type return_consumed_capacity: string
        :param return_consumed_capacity: A value that if set to `TOTAL`, the
            response includes ConsumedCapacity data for tables and indexes. If
            set to `INDEXES`, the response includes ConsumedCapacity for
            indexes. If set to `NONE` (the default), ConsumedCapacity is not
            included in the response.

        :type total_segments: integer
        :param total_segments: For a parallel Scan request, TotalSegments
            represents the total number of segments into which the Scan
            operation will be divided. The value of TotalSegments corresponds
            to the number of application workers that will perform the parallel
            scan. For example, if you want to scan a table using four
            application threads, specify a TotalSegments value of 4.
        The value for TotalSegments must be greater than or equal to 1, and
            less than or equal to 1000000. If you specify a TotalSegments value
            of 1, the Scan operation will be sequential rather than parallel.

        If you specify TotalSegments , you must also specify Segment .

        :type segment: integer
        :param segment: For a parallel Scan request, Segment identifies an
            individual segment to be scanned by an application worker.
        Segment IDs are zero-based, so the first segment is always 0. For
            example, if you want to scan a table using four application
            threads, the first thread specifies a Segment value of 0, the
            second thread specifies 1, and so on.

        The value of LastEvaluatedKey returned from a parallel Scan request
            must be used as ExclusiveStartKey with the same segment ID in a
            subsequent Scan operation.

        The value for Segment must be greater than or equal to 0, and less than
            the value provided for TotalSegments .

        If you specify Segment , you must also specify TotalSegments .

        :type projection_expression: string
        :param projection_expression: A string that identifies one or more
            attributes to retrieve from the table. These attributes can include
            scalars, sets, or elements of a JSON document. The attributes in
            the expression must be separated by commas.
        If no attribute names are specified, then all attributes will be
            returned. If any of the requested attributes are not found, they
            will not appear in the result.

        For more information on projection expressions, go to `Accessing Item
            Attributes`_ in the Amazon DynamoDB Developer Guide .

        :type filter_expression: string
        :param filter_expression: A condition that evaluates the scan results
            and returns only the desired values.
        The condition you specify is applied to the items scanned; any items
            that do not match the expression are not returned.

        :type expression_attribute_names: map
        :param expression_attribute_names: One or more substitution tokens for
            simplifying complex expressions. The following are some use cases
            for using ExpressionAttributeNames :

        + To shorten an attribute name that is very long or unwieldy in an
              expression.
        + To create a placeholder for repeating occurrences of an attribute
              name in an expression.
        + To prevent special characters in an attribute name from being
              misinterpreted in an expression.


        Use the **#** character in an expression to dereference an attribute
            name. For example, consider the following expression:


        + `order.customerInfo.LastName = "Smith" OR order.customerInfo.LastName
              = "Jones"`


        Now suppose that you specified the following for
            ExpressionAttributeNames :


        + `{"#name":"order.customerInfo.LastName"}`


        The expression can now be simplified as follows:


        + `#name = "Smith" OR #name = "Jones"`


        For more information on expression attribute names, go to `Accessing
            Item Attributes`_ in the Amazon DynamoDB Developer Guide .

        :type expression_attribute_values: map
        :param expression_attribute_values: One or more values that can be
            substituted in an expression.
        Use the **:** (colon) character in an expression to dereference an
            attribute value. For example, suppose that you wanted to check
            whether the value of the ProductStatus attribute was one of the
            following:

        `Available | Backordered | Discontinued`

        You would first need to specify ExpressionAttributeValues as follows:

        `{ ":avail":{"S":"Available"}, ":back":{"S":"Backordered"},
            ":disc":{"S":"Discontinued"} }`

        You could then use these values in an expression, such as this:

        `ProductStatus IN (:avail, :back, :disc)`

        For more information on expression attribute values, go to `Specifying
            Conditions`_ in the Amazon DynamoDB Developer Guide .

        """
        params = {'TableName': table_name, }
        if attributes_to_get is not None:
            params['AttributesToGet'] = attributes_to_get
        if limit is not None:
            params['Limit'] = limit
        if select is not None:
            params['Select'] = select
        if scan_filter is not None:
            params['ScanFilter'] = scan_filter
        if conditional_operator is not None:
            params['ConditionalOperator'] = conditional_operator
        if exclusive_start_key is not None:
            params['ExclusiveStartKey'] = exclusive_start_key
        if return_consumed_capacity is not None:
            params['ReturnConsumedCapacity'] = return_consumed_capacity
        if total_segments is not None:
            params['TotalSegments'] = total_segments
        if segment is not None:
            params['Segment'] = segment
        if projection_expression is not None:
            params['ProjectionExpression'] = projection_expression
        if filter_expression is not None:
            params['FilterExpression'] = filter_expression
        if expression_attribute_names is not None:
            params['ExpressionAttributeNames'] = expression_attribute_names
        if expression_attribute_values is not None:
            params['ExpressionAttributeValues'] = expression_attribute_values
        return self.make_request(action='Scan',
                                 body=json.dumps(params))

    def update_item(self, table_name, key, attribute_updates=None,
                    expected=None, conditional_operator=None,
                    return_values=None, return_consumed_capacity=None,
                    return_item_collection_metrics=None,
                    update_expression=None, condition_expression=None,
                    expression_attribute_names=None,
                    expression_attribute_values=None):
        """
        Edits an existing item's attributes, or adds a new item to the
        table if it does not already exist. You can put, delete, or
        add attribute values. You can also perform a conditional
        update (insert a new attribute name-value pair if it doesn't
        exist, or replace an existing name-value pair if it has
        certain expected attribute values).

        You can also return the item's attribute values in the same
        UpdateItem operation using the ReturnValues parameter.

        :type table_name: string
        :param table_name: The name of the table containing the item to update.

        :type key: map
        :param key: The primary key of the item to be updated. Each element
            consists of an attribute name and a value for that attribute.
        For the primary key, you must provide all of the attributes. For
            example, with a hash type primary key, you only need to specify the
            hash attribute. For a hash-and-range type primary key, you must
            specify both the hash attribute and the range attribute.

        :type attribute_updates: map
        :param attribute_updates:
        There is a newer parameter available. Use UpdateExpression instead.
            Note that if you use AttributeUpdates and UpdateExpression at the
            same time, DynamoDB will return a ValidationException exception.

        This parameter can be used for modifying top-level attributes; however,
            it does not support individual list or map elements.

        The names of attributes to be modified, the action to perform on each,
            and the new value for each. If you are updating an attribute that
            is an index key attribute for any indexes on that table, the
            attribute type must match the index key type defined in the
            AttributesDefinition of the table description. You can use
            UpdateItem to update any nonkey attributes.

        Attribute values cannot be null. String and Binary type attributes must
            have lengths greater than zero. Set type attributes must not be
            empty. Requests with empty values will be rejected with a
            ValidationException exception.

        Each AttributeUpdates element consists of an attribute name to modify,
            along with the following:


        + Value - The new value, if applicable, for this attribute.
        + Action - A value that specifies how to perform the update. This
              action is only valid for an existing attribute whose data type is
              Number or is a set; do not use `ADD` for other data types. If an
              item with the specified primary key is found in the table, the
              following values perform the following actions:

            + `PUT` - Adds the specified attribute to the item. If the attribute
                  already exists, it is replaced by the new value.
            + `DELETE` - Removes the attribute and its value, if no value is
                  specified for `DELETE`. The data type of the specified value must
                  match the existing value's data type. If a set of values is
                  specified, then those values are subtracted from the old set. For
                  example, if the attribute value was the set `[a,b,c]` and the
                  `DELETE` action specifies `[a,c]`, then the final attribute value
                  is `[b]`. Specifying an empty set is an error.
            + `ADD` - Adds the specified value to the item, if the attribute does
                  not already exist. If the attribute does exist, then the behavior
                  of `ADD` depends on the data type of the attribute:

                + If the existing attribute is a number, and if Value is also a number,
                      then Value is mathematically added to the existing attribute. If
                      Value is a negative number, then it is subtracted from the existing
                      attribute. If you use `ADD` to increment or decrement a number
                      value for an item that doesn't exist before the update, DynamoDB
                      uses 0 as the initial value. Similarly, if you use `ADD` for an
                      existing item to increment or decrement an attribute value that
                      doesn't exist before the update, DynamoDB uses `0` as the initial
                      value. For example, suppose that the item you want to update
                      doesn't have an attribute named itemcount , but you decide to `ADD`
                      the number `3` to this attribute anyway. DynamoDB will create the
                      itemcount attribute, set its initial value to `0`, and finally add
                      `3` to it. The result will be a new itemcount attribute, with a
                      value of `3`.
                + If the existing data type is a set, and if Value is also a set, then
                      Value is appended to the existing set. For example, if the
                      attribute value is the set `[1,2]`, and the `ADD` action specified
                      `[3]`, then the final attribute value is `[1,2,3]`. An error occurs
                      if an `ADD` action is specified for a set attribute and the
                      attribute type specified does not match the existing set type. Both
                      sets must have the same primitive data type. For example, if the
                      existing data type is a set of strings, Value must also be a set of
                      strings.

          If no item with the specified key is found in the table, the following
              values perform the following actions:

            + `PUT` - Causes DynamoDB to create a new item with the specified
                  primary key, and then adds the attribute.
            + `DELETE` - Nothing happens, because attributes cannot be deleted from
                  a nonexistent item. The operation succeeds, but DynamoDB does not
                  create a new item.
            + `ADD` - Causes DynamoDB to create an item with the supplied primary
                  key and number (or set of numbers) for the attribute value. The
                  only data types allowed are Number and Number Set.



        If you specify any attributes that are part of an index key, then the
            data types for those attributes must match those of the schema in
            the table's attribute definition.

        :type expected: map
        :param expected:
        There is a newer parameter available. Use ConditionExpression instead.
            Note that if you use Expected and ConditionExpression at the same
            time, DynamoDB will return a ValidationException exception.

        This parameter does not support lists or maps.

        A map of attribute/condition pairs. Expected provides a conditional
            block for the UpdateItem operation.

        Each element of Expected consists of an attribute name, a comparison
            operator, and one or more values. DynamoDB compares the attribute
            with the value(s) you supplied, using the comparison operator. For
            each Expected element, the result of the evaluation is either true
            or false.

        If you specify more than one element in the Expected map, then by
            default all of the conditions must evaluate to true. In other
            words, the conditions are ANDed together. (You can use the
            ConditionalOperator parameter to OR the conditions instead. If you
            do this, then at least one of the conditions must evaluate to true,
            rather than all of them.)

        If the Expected map evaluates to true, then the conditional operation
            succeeds; otherwise, it fails.

        Expected contains the following:


        + AttributeValueList - One or more values to evaluate against the
              supplied attribute. The number of values in the list depends on the
              ComparisonOperator being used. For type Number, value comparisons
              are numeric. String value comparisons for greater than, equals, or
              less than are based on ASCII character code values. For example,
              `a` is greater than `A`, and `a` is greater than `B`. For a list of
              code values, see
              `http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters`_.
              For type Binary, DynamoDB treats each byte of the binary data as
              unsigned when it compares binary values, for example when
              evaluating query expressions.
        + ComparisonOperator - A comparator for evaluating attributes in the
              AttributeValueList . When performing the comparison, DynamoDB uses
              strongly consistent reads. The following comparison operators are
              available: `EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL |
              CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN` The following
              are descriptions of each comparison operator.

            + `EQ` : Equal. `EQ` is supported for all datatypes, including lists
                and maps. AttributeValueList can contain only one AttributeValue
                element of type String, Number, Binary, String Set, Number Set, or
                Binary Set. If an item contains an AttributeValue element of a
                different type than the one specified in the request, the value
                does not match. For example, `{"S":"6"}` does not equal
                `{"N":"6"}`. Also, `{"N":"6"}` does not equal `{"NS":["6", "2",
                "1"]}`. > <li>
            + `NE` : Not equal. `NE` is supported for all datatypes, including
                lists and maps. AttributeValueList can contain only one
                AttributeValue of type String, Number, Binary, String Set, Number
                Set, or Binary Set. If an item contains an AttributeValue of a
                different type than the one specified in the request, the value
                does not match. For example, `{"S":"6"}` does not equal
                `{"N":"6"}`. Also, `{"N":"6"}` does not equal `{"NS":["6", "2",
                "1"]}`. > <li>
            + `LE` : Less than or equal. AttributeValueList can contain only one
                AttributeValue element of type String, Number, or Binary (not a set
                type). If an item contains an AttributeValue element of a different
                type than the one specified in the request, the value does not
                match. For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `LT` : Less than. AttributeValueList can contain only one
                AttributeValue of type String, Number, or Binary (not a set type).
                If an item contains an AttributeValue element of a different type
                than the one specified in the request, the value does not match.
                For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `GE` : Greater than or equal. AttributeValueList can contain only one
                AttributeValue element of type String, Number, or Binary (not a set
                type). If an item contains an AttributeValue element of a different
                type than the one specified in the request, the value does not
                match. For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `GT` : Greater than. AttributeValueList can contain only one
                AttributeValue element of type String, Number, or Binary (not a set
                type). If an item contains an AttributeValue element of a different
                type than the one specified in the request, the value does not
                match. For example, `{"S":"6"}` does not equal `{"N":"6"}`. Also,
                `{"N":"6"}` does not compare to `{"NS":["6", "2", "1"]}`. > <li>
            + `NOT_NULL` : The attribute exists. `NOT_NULL` is supported for all
                  datatypes, including lists and maps. This operator tests for the
                  existence of an attribute, not its data type. If the data type of
                  attribute " `a`" is null, and you evaluate it using `NOT_NULL`, the
                  result is a Boolean true . This result is because the attribute "
                  `a`" exists; its data type is not relevant to the `NOT_NULL`
                  comparison operator.
            + `NULL` : The attribute does not exist. `NULL` is supported for all
                  datatypes, including lists and maps. This operator tests for the
                  nonexistence of an attribute, not its data type. If the data type
                  of attribute " `a`" is null, and you evaluate it using `NULL`, the
                  result is a Boolean false . This is because the attribute " `a`"
                  exists; its data type is not relevant to the `NULL` comparison
                  operator.
            + `CONTAINS` : Checks for a subsequence, or value in a set.
                  AttributeValueList can contain only one AttributeValue element of
                  type String, Number, or Binary (not a set type). If the target
                  attribute of the comparison is of type String, then the operator
                  checks for a substring match. If the target attribute of the
                  comparison is of type Binary, then the operator looks for a
                  subsequence of the target that matches the input. If the target
                  attribute of the comparison is a set (" `SS`", " `NS`", or "
                  `BS`"), then the operator evaluates to true if it finds an exact
                  match with any member of the set. CONTAINS is supported for lists:
                  When evaluating " `a CONTAINS b`", " `a`" can be a list; however, "
                  `b`" cannot be a set, a map, or a list.
            + `NOT_CONTAINS` : Checks for absence of a subsequence, or absence of a
                  value in a set. AttributeValueList can contain only one
                  AttributeValue element of type String, Number, or Binary (not a set
                  type). If the target attribute of the comparison is a String, then
                  the operator checks for the absence of a substring match. If the
                  target attribute of the comparison is Binary, then the operator
                  checks for the absence of a subsequence of the target that matches
                  the input. If the target attribute of the comparison is a set ("
                  `SS`", " `NS`", or " `BS`"), then the operator evaluates to true if
                  it does not find an exact match with any member of the set.
                  NOT_CONTAINS is supported for lists: When evaluating " `a NOT
                  CONTAINS b`", " `a`" can be a list; however, " `b`" cannot be a
                  set, a map, or a list.
            + `BEGINS_WITH` : Checks for a prefix. AttributeValueList can contain
                only one AttributeValue of type String or Binary (not a Number or a
                set type). The target attribute of the comparison must be of type
                String or Binary (not a Number or a set type). > <li>
            + `IN` : Checks for matching elements within two sets.
                  AttributeValueList can contain one or more AttributeValue elements
                  of type String, Number, or Binary (not a set type). These
                  attributes are compared against an existing set type attribute of
                  an item. If any elements of the input set are present in the item
                  attribute, the expression evaluates to true.
            + `BETWEEN` : Greater than or equal to the first value, and less than
                  or equal to the second value. AttributeValueList must contain two
                  AttributeValue elements of the same type, either String, Number, or
                  Binary (not a set type). A target attribute matches if the target
                  value is greater than, or equal to, the first element and less
                  than, or equal to, the second element. If an item contains an
                  AttributeValue element of a different type than the one specified
                  in the request, the value does not match. For example, `{"S":"6"}`
                  does not compare to `{"N":"6"}`. Also, `{"N":"6"}` does not compare
                  to `{"NS":["6", "2", "1"]}`



        For usage examples of AttributeValueList and ComparisonOperator , see
            `Legacy Conditional Parameters`_ in the Amazon DynamoDB Developer
            Guide .

        For backward compatibility with previous DynamoDB releases, the
            following parameters can be used instead of AttributeValueList and
            ComparisonOperator :


        + Value - A value for DynamoDB to compare with an attribute.
        + Exists - A Boolean value that causes DynamoDB to evaluate the value
              before attempting the conditional operation:

            + If Exists is `True`, DynamoDB will check to see if that attribute
                  value already exists in the table. If it is found, then the
                  condition evaluates to true; otherwise the condition evaluate to
                  false.
            + If Exists is `False`, DynamoDB assumes that the attribute value does
                  not exist in the table. If in fact the value does not exist, then
                  the assumption is valid and the condition evaluates to true. If the
                  value is found, despite the assumption that it does not exist, the
                  condition evaluates to false.
          Note that the default value for Exists is `True`.


        The Value and Exists parameters are incompatible with
            AttributeValueList and ComparisonOperator . Note that if you use
            both sets of parameters at once, DynamoDB will return a
            ValidationException exception.

        :type conditional_operator: string
        :param conditional_operator:
        There is a newer parameter available. Use ConditionExpression instead.
            Note that if you use ConditionalOperator and ConditionExpression at
            the same time, DynamoDB will return a ValidationException
            exception.

        This parameter does not support lists or maps.

        A logical operator to apply to the conditions in the Expected map:


        + `AND` - If all of the conditions evaluate to true, then the entire
              map evaluates to true.
        + `OR` - If at least one of the conditions evaluate to true, then the
              entire map evaluates to true.


        If you omit ConditionalOperator , then `AND` is the default.

        The operation will succeed only if the entire map evaluates to true.

        :type return_values: string
        :param return_values:
        Use ReturnValues if you want to get the item attributes as they
            appeared either before or after they were updated. For UpdateItem ,
            the valid values are:


        + `NONE` - If ReturnValues is not specified, or if its value is `NONE`,
              then nothing is returned. (This setting is the default for
              ReturnValues .)
        + `ALL_OLD` - If UpdateItem overwrote an attribute name-value pair,
              then the content of the old item is returned.
        + `UPDATED_OLD` - The old versions of only the updated attributes are
              returned.
        + `ALL_NEW` - All of the attributes of the new version of the item are
              returned.
        + `UPDATED_NEW` - The new versions of only the updated attributes are
              returned.

        :type return_consumed_capacity: string
        :param return_consumed_capacity: A value that if set to `TOTAL`, the
            response includes ConsumedCapacity data for tables and indexes. If
            set to `INDEXES`, the response includes ConsumedCapacity for
            indexes. If set to `NONE` (the default), ConsumedCapacity is not
            included in the response.

        :type return_item_collection_metrics: string
        :param return_item_collection_metrics: A value that if set to `SIZE`,
            the response includes statistics about item collections, if any,
            that were modified during the operation are returned in the
            response. If set to `NONE` (the default), no statistics are
            returned.

        :type update_expression: string
        :param update_expression: An expression that defines one or more
            attributes to be updated, the action to be performed on them, and
            new value(s) for them.
        The following action values are available for UpdateExpression .


        + `SET` - Adds one or more attributes and values to an item. If any of
              these attribute already exist, they are replaced by the new values.
              You can also use `SET` to add or subtract from an attribute that is
              of type Number. `SET` supports the following functions:

            + `if_not_exists (path, operand)` - if the item does not contain an
                  attribute at the specified path, then `if_not_exists` evaluates to
                  operand; otherwise, it evaluates to path. You can use this function
                  to avoid overwriting an attribute that may already be present in
                  the item.
            + `list_append (operand, operand)` - evaluates to a list with a new
                  element added to it. You can append the new element to the start or
                  the end of the list by reversing the order of the operands.
          These function names are case-sensitive.
        + `REMOVE` - Removes one or more attributes from an item.
        + `ADD` - Adds the specified value to the item, if the attribute does
              not already exist. If the attribute does exist, then the behavior
              of `ADD` depends on the data type of the attribute:

            + If the existing attribute is a number, and if Value is also a number,
                  then Value is mathematically added to the existing attribute. If
                  Value is a negative number, then it is subtracted from the existing
                  attribute. If you use `ADD` to increment or decrement a number
                  value for an item that doesn't exist before the update, DynamoDB
                  uses `0` as the initial value. Similarly, if you use `ADD` for an
                  existing item to increment or decrement an attribute value that
                  doesn't exist before the update, DynamoDB uses `0` as the initial
                  value. For example, suppose that the item you want to update
                  doesn't have an attribute named itemcount , but you decide to `ADD`
                  the number `3` to this attribute anyway. DynamoDB will create the
                  itemcount attribute, set its initial value to `0`, and finally add
                  `3` to it. The result will be a new itemcount attribute in the
                  item, with a value of `3`.
            + If the existing data type is a set and if Value is also a set, then
                  Value is added to the existing set. For example, if the attribute
                  value is the set `[1,2]`, and the `ADD` action specified `[3]`,
                  then the final attribute value is `[1,2,3]`. An error occurs if an
                  `ADD` action is specified for a set attribute and the attribute
                  type specified does not match the existing set type. Both sets must
                  have the same primitive data type. For example, if the existing
                  data type is a set of strings, the Value must also be a set of
                  strings.
          The `ADD` action only supports Number and set data types. In addition,
              `ADD` can only be used on top-level attributes, not nested
              attributes.
        + `DELETE` - Deletes an element from a set. If a set of values is
              specified, then those values are subtracted from the old set. For
              example, if the attribute value was the set `[a,b,c]` and the
              `DELETE` action specifies `[a,c]`, then the final attribute value
              is `[b]`. Specifying an empty set is an error. The `DELETE` action
              only supports Number and set data types. In addition, `DELETE` can
              only be used on top-level attributes, not nested attributes.


        You can have many actions in a single expression, such as the
            following: `SET a=:value1, b=:value2 DELETE :value3, :value4,
            :value5`

        For more information on update expressions, go to `Modifying Items and
            Attributes`_ in the Amazon DynamoDB Developer Guide .

        :type condition_expression: string
        :param condition_expression: A condition that must be satisfied in
            order for a conditional update to succeed.
        An expression can contain any of the following:


        + Boolean functions: `attribute_exists | attribute_not_exists |
              contains | begins_with` These function names are case-sensitive.
        + Comparison operators: ` = | <> | < | > | <=
              | >= | BETWEEN | IN`
        + Logical operators: `AND | OR | NOT`


        For more information on condition expressions, go to `Specifying
            Conditions`_ in the Amazon DynamoDB Developer Guide .

        :type expression_attribute_names: map
        :param expression_attribute_names: One or more substitution tokens for
            simplifying complex expressions. The following are some use cases
            for using ExpressionAttributeNames :

        + To shorten an attribute name that is very long or unwieldy in an
              expression.
        + To create a placeholder for repeating occurrences of an attribute
              name in an expression.
        + To prevent special characters in an attribute name from being
              misinterpreted in an expression.


        Use the **#** character in an expression to dereference an attribute
            name. For example, consider the following expression:


        + `order.customerInfo.LastName = "Smith" OR order.customerInfo.LastName
              = "Jones"`


        Now suppose that you specified the following for
            ExpressionAttributeNames :


        + `{"#name":"order.customerInfo.LastName"}`


        The expression can now be simplified as follows:


        + `#name = "Smith" OR #name = "Jones"`


        For more information on expression attribute names, go to `Accessing
            Item Attributes`_ in the Amazon DynamoDB Developer Guide .

        :type expression_attribute_values: map
        :param expression_attribute_values: One or more values that can be
            substituted in an expression.
        Use the **:** (colon) character in an expression to dereference an
            attribute value. For example, suppose that you wanted to check
            whether the value of the ProductStatus attribute was one of the
            following:

        `Available | Backordered | Discontinued`

        You would first need to specify ExpressionAttributeValues as follows:

        `{ ":avail":{"S":"Available"}, ":back":{"S":"Backordered"},
            ":disc":{"S":"Discontinued"} }`

        You could then use these values in an expression, such as this:

        `ProductStatus IN (:avail, :back, :disc)`

        For more information on expression attribute values, go to `Specifying
            Conditions`_ in the Amazon DynamoDB Developer Guide .

        """
        params = {'TableName': table_name, 'Key': key, }
        if attribute_updates is not None:
            params['AttributeUpdates'] = attribute_updates
        if expected is not None:
            params['Expected'] = expected
        if conditional_operator is not None:
            params['ConditionalOperator'] = conditional_operator
        if return_values is not None:
            params['ReturnValues'] = return_values
        if return_consumed_capacity is not None:
            params['ReturnConsumedCapacity'] = return_consumed_capacity
        if return_item_collection_metrics is not None:
            params['ReturnItemCollectionMetrics'] = return_item_collection_metrics
        if update_expression is not None:
            params['UpdateExpression'] = update_expression
        if condition_expression is not None:
            params['ConditionExpression'] = condition_expression
        if expression_attribute_names is not None:
            params['ExpressionAttributeNames'] = expression_attribute_names
        if expression_attribute_values is not None:
            params['ExpressionAttributeValues'] = expression_attribute_values
        return self.make_request(action='UpdateItem',
                                 body=json.dumps(params))

    def update_table(self, table_name, provisioned_throughput=None,
                     global_secondary_index_updates=None,
                     attribute_definitions=None):
        """
        Updates the provisioned throughput for the given table, or
        manages the global secondary indexes on the table.

        You can increase or decrease the table's provisioned
        throughput values within the maximums and minimums listed in
        the `Limits`_ section in the Amazon DynamoDB Developer Guide .

        In addition, you can use UpdateTable to add, modify or delete
        global secondary indexes on the table. For more information,
        see `Managing Global Secondary Indexes`_ in the Amazon
        DynamoDB Developer Guide .

        The table must be in the `ACTIVE` state for UpdateTable to
        succeed. UpdateTable is an asynchronous operation; while
        executing the operation, the table is in the `UPDATING` state.
        While the table is in the `UPDATING` state, the table still
        has the provisioned throughput from before the call. The
        table's new provisioned throughput settings go into effect
        when the table returns to the `ACTIVE` state; at that point,
        the UpdateTable operation is complete.

        :type attribute_definitions: list
        :param attribute_definitions: An array of attributes that describe the
            key schema for the table and indexes. If you are adding a new
            global secondary index to the table, AttributeDefinitions must
            include the key element(s) of the new index.

        :type table_name: string
        :param table_name: The name of the table to be updated.

        :type provisioned_throughput: dict
        :param provisioned_throughput: Represents the provisioned throughput
            settings for a specified table or index. The settings can be
            modified using the UpdateTable operation.
        For current minimum and maximum provisioned throughput values, see
            `Limits`_ in the Amazon DynamoDB Developer Guide .

        :type global_secondary_index_updates: list
        :param global_secondary_index_updates:
        An array of one or more global secondary indexes for the table. For
            each index in the array, you can specify one action:


        + Create - add a new global secondary index to the table.
        + Update - modify the provisioned throughput settings of an existing
              global secondary index.
        + Delete - remove a global secondary index from the table.

        """
        params = {'TableName': table_name, }
        if attribute_definitions is not None:
            params['AttributeDefinitions'] = attribute_definitions
        if provisioned_throughput is not None:
            params['ProvisionedThroughput'] = provisioned_throughput
        if global_secondary_index_updates is not None:
            params['GlobalSecondaryIndexUpdates'] = global_secondary_index_updates
        return self.make_request(action='UpdateTable',
                                 body=json.dumps(params))

    def make_request(self, action, body):
        headers = {
            'X-Amz-Target': '%s.%s' % (self.TargetPrefix, action),
            'Host': self.host,
            'Content-Type': 'application/x-amz-json-1.0',
            'Content-Length': str(len(body)),
        }
        http_request = self.build_base_http_request(
            method='POST', path='/', auth_path='/', params={},
            headers=headers, data=body, host=self.host)
        response = self._mexe(http_request, sender=None,
                              override_num_retries=self.NumberRetries,
                              retry_handler=self._retry_handler)
        response_body = response.read().decode('utf-8')
        boto.log.debug(response_body)
        if response.status == 200:
            if response_body:
                return json.loads(response_body)
        else:
            json_body = json.loads(response_body)
            fault_name = json_body.get('__type', None)
            exception_class = self._faults.get(fault_name, self.ResponseError)
            raise exception_class(response.status, response.reason,
                                  body=json_body)

    def _retry_handler(self, response, i, next_sleep):
        status = None
        boto.log.debug("Saw HTTP status: %s" % response.status)
        if response.status == 400:
            response_body = response.read().decode('utf-8')
            boto.log.debug(response_body)
            data = json.loads(response_body)
            if 'ProvisionedThroughputExceededException' in data.get('__type'):
                self.throughput_exceeded_events += 1
                msg = "%s, retry attempt %s" % (
                    'ProvisionedThroughputExceededException',
                    i
                )
                next_sleep = self._truncated_exponential_time(i)
                i += 1
                status = (msg, i, next_sleep)
                if i == self.NumberRetries:
                    # If this was our last retry attempt, raise
                    # a specific error saying that the throughput
                    # was exceeded.
                    raise exceptions.ProvisionedThroughputExceededException(
                        response.status, response.reason, data)
            elif 'ConditionalCheckFailedException' in data.get('__type'):
                raise exceptions.ConditionalCheckFailedException(
                    response.status, response.reason, data)
            elif 'ValidationException' in data.get('__type'):
                raise exceptions.ValidationException(
                    response.status, response.reason, data)
            else:
                raise self.ResponseError(response.status, response.reason,
                                         data)
        expected_crc32 = response.getheader('x-amz-crc32')
        if self._validate_checksums and expected_crc32 is not None:
            boto.log.debug('Validating crc32 checksum for body: %s',
                           response.read())
            actual_crc32 = crc32(response.read()) & 0xffffffff
            expected_crc32 = int(expected_crc32)
            if actual_crc32 != expected_crc32:
                msg = ("The calculated checksum %s did not match the expected "
                       "checksum %s" % (actual_crc32, expected_crc32))
                status = (msg, i + 1, self._truncated_exponential_time(i))
        return status

    def _truncated_exponential_time(self, i):
        if i == 0:
            next_sleep = 0
        else:
            next_sleep = min(0.05 * (2 ** i),
                             boto.config.get('Boto', 'max_retry_delay', 60))
        return next_sleep

`kwargs['host'] = kwargs.get('host') or region.endpoint`, so at least it's consistently defined - and if someone passes 0 or False, it will behave the same. Or if you prefer the conditional, `if not kwargs.get('host')`. Just a thought. The change looks great by itself.