'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.'

def batch_get_item(self, request_items, return_consumed_capacity=None):

    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))
