text: # sqlite/base.py
  # Copyright (C) 2005-2015 the SQLAlchemy authors and contributors
  # <see AUTHORS file>
  #
  # This module is part of SQLAlchemy and is released under
  # the MIT License: http://www.opensource.org/licenses/mit-license.php
  
  """
  .. dialect:: sqlite
      :name: SQLite
  
  
  Date and Time Types
  -------------------
  
  SQLite does not have built-in DATE, TIME, or DATETIME types, and pysqlite does
  not provide out of the box functionality for translating values between Python
  `datetime` objects and a SQLite-supported format. SQLAlchemy's own
  :class:`~sqlalchemy.types.DateTime` and related types provide date formatting
  and parsing functionality when SQlite is used. The implementation classes are
  :class:`~.sqlite.DATETIME`, :class:`~.sqlite.DATE` and :class:`~.sqlite.TIME`.
  These types represent dates and times as ISO formatted strings, which also
  nicely support ordering. There's no reliance on typical "libc" internals for
  these functions so historical dates are fully supported.
  
  .. _sqlite_autoincrement:
  
  SQLite Auto Incrementing Behavior
  ----------------------------------
  
  Background on SQLite's autoincrement is at: http://sqlite.org/autoinc.html
  
  Two things to note:
  
  * The AUTOINCREMENT keyword is **not** required for SQLite tables to
    generate primary key values automatically. AUTOINCREMENT only means that the
    algorithm used to generate ROWID values should be slightly different.
  * SQLite does **not** generate primary key (i.e. ROWID) values, even for
    one column, if the table has a composite (i.e. multi-column) primary key.
    This is regardless of the AUTOINCREMENT keyword being present or not.
  
  To specifically render the AUTOINCREMENT keyword on the primary key column
  when rendering DDL, add the flag ``sqlite_autoincrement=True`` to the Table
  construct::
  
      Table('sometable', metadata,
              Column('id', Integer, primary_key=True),
              sqlite_autoincrement=True)
  
  
  .. _sqlite_concurrency:
  
  Database Locking Behavior / Concurrency
  ---------------------------------------
  
  SQLite is not designed for a high level of write concurrency. The database
  itself, being a file, is locked completely during write operations within
  transactions, meaning exactly one "connection" (in reality a file handle)
  has exclusive access to the database during this period - all other
  "connections" will be blocked during this time.
  
  The Python DBAPI specification also calls for a connection model that is
  always in a transaction; there is no ``connection.begin()`` method,
  only ``connection.commit()`` and ``connection.rollback()``, upon which a
  new transaction is to be begun immediately.  This may seem to imply
  that the SQLite driver would in theory allow only a single filehandle on a
  particular database file at any time; however, there are several
  factors both within SQlite itself as well as within the pysqlite driver
  which loosen this restriction significantly.
  
  However, no matter what locking modes are used, SQLite will still always
  lock the database file once a transaction is started and DML (e.g. INSERT,
  UPDATE, DELETE) has at least been emitted, and this will block
  other transactions at least at the point that they also attempt to emit DML.
  By default, the length of time on this block is very short before it times out
  with an error.
  
  This behavior becomes more critical when used in conjunction with the
  SQLAlchemy ORM.  SQLAlchemy's :class:`.Session` object by default runs
  within a transaction, and with its autoflush model, may emit DML preceding
  any SELECT statement.   This may lead to a SQLite database that locks
  more quickly than is expected.   The locking mode of SQLite and the pysqlite
  driver can be manipulated to some degree, however it should be noted that
  achieving a high degree of write-concurrency with SQLite is a losing battle.
  
  For more information on SQLite's lack of write concurrency by design, please
  see
  `Situations Where Another RDBMS May Work Better - High Concurrency
  <http://www.sqlite.org/whentouse.html>`_ near the bottom of the page.
  
  The following subsections introduce areas that are impacted by SQLite's
  file-based architecture and additionally will usually require workarounds to
  work when using the pysqlite driver.
  
  .. _sqlite_isolation_level:
  
  Transaction Isolation Level
  ----------------------------
  
  SQLite supports "transaction isolation" in a non-standard way, along two
  axes.  One is that of the `PRAGMA read_uncommitted <http://www.sqlite.org/pragma.html#pragma_read_uncommitted>`_
  instruction.   This setting can essentially switch SQLite between its
  default mode of ``SERIALIZABLE`` isolation, and a "dirty read" isolation
  mode normally referred to as ``READ UNCOMMITTED``.
  
  SQLAlchemy ties into this PRAGMA statement using the
  :paramref:`.create_engine.isolation_level` parameter of :func:`.create_engine`.
  Valid values for this parameter when used with SQLite are ``"SERIALIZABLE"``
  and ``"READ UNCOMMITTED"`` corresponding to a value of 0 and 1, respectively.
  SQLite defaults to ``SERIALIZABLE``, however its behavior is impacted by
  the pysqlite driver's default behavior.
  
  The other axis along which SQLite's transactional locking is impacted is
  via the nature of the ``BEGIN`` statement used.   The three varieties
  are "deferred", "immediate", and "exclusive", as described at
  `BEGIN TRANSACTION <http://sqlite.org/lang_transaction.html>`_.   A straight
  ``BEGIN`` statement uses the "deferred" mode, where the the database file is
  not locked until the first read or write operation, and read access remains
  open to other transactions until the first write operation.  But again,
  it is critical to note that the pysqlite driver interferes with this behavior
  by *not even emitting BEGIN* until the first write operation.
  
  .. warning::
  
      SQLite's transactional scope is impacted by unresolved
      issues in the pysqlite driver, which defers BEGIN statements to a greater
      degree than is often feasible. See the section :ref:`pysqlite_serializable`
      for techniques to work around this behavior.
  
  SAVEPOINT Support
  ----------------------------
  
  SQLite supports SAVEPOINTs, which only function once a transaction is
  begun.   SQLAlchemy's SAVEPOINT support is available using the
  :meth:`.Connection.begin_nested` method at the Core level, and
  :meth:`.Session.begin_nested` at the ORM level.   However, SAVEPOINTs
  won't work at all with pysqlite unless workarounds are taken.
  
  .. warning::
  
      SQLite's SAVEPOINT feature is impacted by unresolved
      issues in the pysqlite driver, which defers BEGIN statements to a greater
      degree than is often feasible. See the section :ref:`pysqlite_serializable`
      for techniques to work around this behavior.
  
  Transactional DDL
  ----------------------------
  
  The SQLite database supports transactional :term:`DDL` as well.
  In this case, the pysqlite driver is not only failing to start transactions,
  it also is ending any existing transction when DDL is detected, so again,
  workarounds are required.
  
  .. warning::
  
      SQLite's transactional DDL is impacted by unresolved issues
      in the pysqlite driver, which fails to emit BEGIN and additionally
      forces a COMMIT to cancel any transaction when DDL is encountered.
      See the section :ref:`pysqlite_serializable`
      for techniques to work around this behavior.
  
  .. _sqlite_foreign_keys:
  
  Foreign Key Support
  -------------------
  
  SQLite supports FOREIGN KEY syntax when emitting CREATE statements for tables,
  however by default these constraints have no effect on the operation of the
  table.
  
  Constraint checking on SQLite has three prerequisites:
  
  * At least version 3.6.19 of SQLite must be in use
  * The SQLite library must be compiled *without* the SQLITE_OMIT_FOREIGN_KEY
    or SQLITE_OMIT_TRIGGER symbols enabled.
  * The ``PRAGMA foreign_keys = ON`` statement must be emitted on all
    connections before use.
  
  SQLAlchemy allows for the ``PRAGMA`` statement to be emitted automatically for
  new connections through the usage of events::
  
      from sqlalchemy.engine import Engine
      from sqlalchemy import event
  
      @event.listens_for(Engine, "connect")
      def set_sqlite_pragma(dbapi_connection, connection_record):
          cursor = dbapi_connection.cursor()
          cursor.execute("PRAGMA foreign_keys=ON")
          cursor.close()
  
  .. seealso::
  
      `SQLite Foreign Key Support <http://www.sqlite.org/foreignkeys.html>`_
      - on the SQLite web site.
  
      :ref:`event_toplevel` - SQLAlchemy event API.
  
  .. _sqlite_type_reflection:
  
  Type Reflection
  ---------------
  
  SQLite types are unlike those of most other database backends, in that
  the string name of the type usually does not correspond to a "type" in a
  one-to-one fashion.  Instead, SQLite links per-column typing behavior
  to one of five so-called "type affinities" based on a string matching
  pattern for the type.
  
  SQLAlchemy's reflection process, when inspecting types, uses a simple
  lookup table to link the keywords returned to provided SQLAlchemy types.
  This lookup table is present within the SQLite dialect as it is for all
  other dialects.  However, the SQLite dialect has a different "fallback"
  routine for when a particular type name is not located in the lookup map;
  it instead implements the SQLite "type affinity" scheme located at
  http://www.sqlite.org/datatype3.html section 2.1.
  
  The provided typemap will make direct associations from an exact string
  name match for the following types:
  
  :class:`~.types.BIGINT`, :class:`~.types.BLOB`,
  :class:`~.types.BOOLEAN`, :class:`~.types.BOOLEAN`,
  :class:`~.types.CHAR`, :class:`~.types.DATE`,
  :class:`~.types.DATETIME`, :class:`~.types.FLOAT`,
  :class:`~.types.DECIMAL`, :class:`~.types.FLOAT`,
  :class:`~.types.INTEGER`, :class:`~.types.INTEGER`,
  :class:`~.types.NUMERIC`, :class:`~.types.REAL`,
  :class:`~.types.SMALLINT`, :class:`~.types.TEXT`,
  :class:`~.types.TIME`, :class:`~.types.TIMESTAMP`,
  :class:`~.types.VARCHAR`, :class:`~.types.NVARCHAR`,
  :class:`~.types.NCHAR`
  
  When a type name does not match one of the above types, the "type affinity"
  lookup is used instead:
  
  * :class:`~.types.INTEGER` is returned if the type name includes the
    string ``INT``
  * :class:`~.types.TEXT` is returned if the type name includes the
    string ``CHAR``, ``CLOB`` or ``TEXT``
  * :class:`~.types.NullType` is returned if the type name includes the
    string ``BLOB``
  * :class:`~.types.REAL` is returned if the type name includes the string
    ``REAL``, ``FLOA`` or ``DOUB``.
  * Otherwise, the :class:`~.types.NUMERIC` type is used.
  
  .. versionadded:: 0.9.3 Support for SQLite type affinity rules when reflecting
     columns.
  
  
  .. _sqlite_partial_index:
  
  Partial Indexes
  ---------------
  
  A partial index, e.g. one which uses a WHERE clause, can be specified
  with the DDL system using the argument ``sqlite_where``::
  
      tbl = Table('testtbl', m, Column('data', Integer))
      idx = Index('test_idx1', tbl.c.data,
                  sqlite_where=and_(tbl.c.data > 5, tbl.c.data < 10))
  
  The index will be rendered at create time as::
  
      CREATE INDEX test_idx1 ON testtbl (data)
      WHERE data > 5 AND data < 10
  
  .. versionadded:: 0.9.9
  
  """
  
  import datetime
  import re
  
  from ... import processors
  from ... import sql, exc
  from ... import types as sqltypes, schema as sa_schema
  from ... import util
  from ...engine import default, reflection
  from ...sql import compiler
  
  from ...types import (BLOB, BOOLEAN, CHAR, DATE, DECIMAL, FLOAT,
                        INTEGER, REAL, NUMERIC, SMALLINT, TEXT,
                        TIMESTAMP, VARCHAR)
  
  
  class _DateTimeMixin(object):
      _reg = None
      _storage_format = None
  
      def __init__(self, storage_format=None, regexp=None, **kw):
          super(_DateTimeMixin, self).__init__(**kw)
          if regexp is not None:
              self._reg = re.compile(regexp)
          if storage_format is not None:
              self._storage_format = storage_format
  
      def adapt(self, cls, **kw):
          if issubclass(cls, _DateTimeMixin):
              if self._storage_format:
                  kw["storage_format"] = self._storage_format
              if self._reg:
                  kw["regexp"] = self._reg
          return super(_DateTimeMixin, self).adapt(cls, **kw)
  
      def literal_processor(self, dialect):
          bp = self.bind_processor(dialect)
  
          def process(value):
              return "'%s'" % bp(value)
          return process
  
  
  class DATETIME(_DateTimeMixin, sqltypes.DateTime):
      """Represent a Python datetime object in SQLite using a string.
  
      The default string storage format is::
  
          "%(year)04d-%(month)02d-%(day)02d %(hour)02d:%(min)02d:\
  %(second)02d.%(microsecond)06d"
  
      e.g.::
  
          2011-03-15 12:05:57.10558
  
      The storage format can be customized to some degree using the
      ``storage_format`` and ``regexp`` parameters, such as::
  
          import re
          from sqlalchemy.dialects.sqlite import DATETIME
  
          dt = DATETIME(
              storage_format="%(year)04d/%(month)02d/%(day)02d %(hour)02d:\
  %(min)02d:%(second)02d",
              regexp=r"(\d+)/(\d+)/(\d+) (\d+)-(\d+)-(\d+)"
          )
  
      :param storage_format: format string which will be applied to the dict
       with keys year, month, day, hour, minute, second, and microsecond.
  
      :param regexp: regular expression which will be applied to incoming result
       rows. If the regexp contains named groups, the resulting match dict is
       applied to the Python datetime() constructor as keyword arguments.
       Otherwise, if positional groups are used, the datetime() constructor
       is called with positional arguments via
       ``*map(int, match_obj.groups(0))``.
      """
  
      _storage_format = (
          "%(year)04d-%(month)02d-%(day)02d "
          "%(hour)02d:%(minute)02d:%(second)02d.%(microsecond)06d"
      )
  
      def __init__(self, *args, **kwargs):
          truncate_microseconds = kwargs.pop('truncate_microseconds', False)
          super(DATETIME, self).__init__(*args, **kwargs)
          if truncate_microseconds:
              assert 'storage_format' not in kwargs, "You can specify only "\
                  "one of truncate_microseconds or storage_format."
              assert 'regexp' not in kwargs, "You can specify only one of "\
                  "truncate_microseconds or regexp."
              self._storage_format = (
                  "%(year)04d-%(month)02d-%(day)02d "
                  "%(hour)02d:%(minute)02d:%(second)02d"
              )
  
      def bind_processor(self, dialect):
          datetime_datetime = datetime.datetime
          datetime_date = datetime.date
          format = self._storage_format
  
          def process(value):
              if value is None:
                  return None
              elif isinstance(value, datetime_datetime):
                  return format % {
                      'year': value.year,
                      'month': value.month,
                      'day': value.day,
                      'hour': value.hour,
                      'minute': value.minute,
                      'second': value.second,
                      'microsecond': value.microsecond,
                  }
              elif isinstance(value, datetime_date):
                  return format % {
                      'year': value.year,
                      'month': value.month,
                      'day': value.day,
                      'hour': 0,
                      'minute': 0,
                      'second': 0,
                      'microsecond': 0,
                  }
              else:
                  raise TypeError("SQLite DateTime type only accepts Python "
                                  "datetime and date objects as input.")
          return process
  
      def result_processor(self, dialect, coltype):
          if self._reg:
              return processors.str_to_datetime_processor_factory(
                  self._reg, datetime.datetime)
          else:
              return processors.str_to_datetime
  
  
  class DATE(_DateTimeMixin, sqltypes.Date):
      """Represent a Python date object in SQLite using a string.
  
      The default string storage format is::
  
          "%(year)04d-%(month)02d-%(day)02d"
  
      e.g.::
  
          2011-03-15
  
      The storage format can be customized to some degree using the
      ``storage_format`` and ``regexp`` parameters, such as::
  
          import re
          from sqlalchemy.dialects.sqlite import DATE
  
          d = DATE(
                  storage_format="%(month)02d/%(day)02d/%(year)04d",
                  regexp=re.compile("(?P<month>\d+)/(?P<day>\d+)/(?P<year>\d+)")
              )
  
      :param storage_format: format string which will be applied to the
       dict with keys year, month, and day.
  
      :param regexp: regular expression which will be applied to
       incoming result rows. If the regexp contains named groups, the
       resulting match dict is applied to the Python date() constructor
       as keyword arguments. Otherwise, if positional groups are used, the
       date() constructor is called with positional arguments via
       ``*map(int, match_obj.groups(0))``.
      """
  
      _storage_format = "%(year)04d-%(month)02d-%(day)02d"
  
      def bind_processor(self, dialect):
          datetime_date = datetime.date
          format = self._storage_format
  
          def process(value):
              if value is None:
                  return None
              elif isinstance(value, datetime_date):
                  return format % {
                      'year': value.year,
                      'month': value.month,
                      'day': value.day,
                  }
              else:
                  raise TypeError("SQLite Date type only accepts Python "
                                  "date objects as input.")
          return process
  
      def result_processor(self, dialect, coltype):
          if self._reg:
              return processors.str_to_datetime_processor_factory(
                  self._reg, datetime.date)
          else:
              return processors.str_to_date
  
  
  class TIME(_DateTimeMixin, sqltypes.Time):
      """Represent a Python time object in SQLite using a string.
  
      The default string storage format is::
  
          "%(hour)02d:%(minute)02d:%(second)02d.%(microsecond)06d"
  
      e.g.::
  
          12:05:57.10558
  
      The storage format can be customized to some degree using the
      ``storage_format`` and ``regexp`` parameters, such as::
  
          import re
          from sqlalchemy.dialects.sqlite import TIME
  
          t = TIME(
              storage_format="%(hour)02d-%(minute)02d-%(second)02d-\
  %(microsecond)06d",
              regexp=re.compile("(\d+)-(\d+)-(\d+)-(?:-(\d+))?")
          )
  
      :param storage_format: format string which will be applied to the dict
       with keys hour, minute, second, and microsecond.
  
      :param regexp: regular expression which will be applied to incoming result
       rows. If the regexp contains named groups, the resulting match dict is
       applied to the Python time() constructor as keyword arguments. Otherwise,
       if positional groups are used, the time() constructor is called with
       positional arguments via ``*map(int, match_obj.groups(0))``.
      """
  
      _storage_format = "%(hour)02d:%(minute)02d:%(second)02d.%(microsecond)06d"
  
      def __init__(self, *args, **kwargs):
          truncate_microseconds = kwargs.pop('truncate_microseconds', False)
          super(TIME, self).__init__(*args, **kwargs)
          if truncate_microseconds:
              assert 'storage_format' not in kwargs, "You can specify only "\
                  "one of truncate_microseconds or storage_format."
              assert 'regexp' not in kwargs, "You can specify only one of "\
                  "truncate_microseconds or regexp."
              self._storage_format = "%(hour)02d:%(minute)02d:%(second)02d"
  
      def bind_processor(self, dialect):
          datetime_time = datetime.time
          format = self._storage_format
  
          def process(value):
              if value is None:
                  return None
              elif isinstance(value, datetime_time):
                  return format % {
                      'hour': value.hour,
                      'minute': value.minute,
                      'second': value.second,
                      'microsecond': value.microsecond,
                  }
              else:
                  raise TypeError("SQLite Time type only accepts Python "
                                  "time objects as input.")
          return process
  
      def result_processor(self, dialect, coltype):
          if self._reg:
              return processors.str_to_datetime_processor_factory(
                  self._reg, datetime.time)
          else:
              return processors.str_to_time
  
  colspecs = {
      sqltypes.Date: DATE,
      sqltypes.DateTime: DATETIME,
      sqltypes.Time: TIME,
  }
  
  ischema_names = {
      'BIGINT': sqltypes.BIGINT,
      'BLOB': sqltypes.BLOB,
      'BOOL': sqltypes.BOOLEAN,
      'BOOLEAN': sqltypes.BOOLEAN,
      'CHAR': sqltypes.CHAR,
      'DATE': sqltypes.DATE,
      'DATETIME': sqltypes.DATETIME,
      'DOUBLE': sqltypes.FLOAT,
      'DECIMAL': sqltypes.DECIMAL,
      'FLOAT': sqltypes.FLOAT,
      'INT': sqltypes.INTEGER,
      'INTEGER': sqltypes.INTEGER,
      'NUMERIC': sqltypes.NUMERIC,
      'REAL': sqltypes.REAL,
      'SMALLINT': sqltypes.SMALLINT,
      'TEXT': sqltypes.TEXT,
      'TIME': sqltypes.TIME,
      'TIMESTAMP': sqltypes.TIMESTAMP,
      'VARCHAR': sqltypes.VARCHAR,
      'NVARCHAR': sqltypes.NVARCHAR,
      'NCHAR': sqltypes.NCHAR,
  }
  
  
  class SQLiteCompiler(compiler.SQLCompiler):
      extract_map = util.update_copy(
          compiler.SQLCompiler.extract_map,
          {
              'month': '%m',
              'day': '%d',
              'year': '%Y',
              'second': '%S',
              'hour': '%H',
              'doy': '%j',
              'minute': '%M',
              'epoch': '%s',
              'dow': '%w',
              'week': '%W',
          })
  
      def visit_now_func(self, fn, **kw):
          return "CURRENT_TIMESTAMP"
  
      def visit_localtimestamp_func(self, func, **kw):
          return 'DATETIME(CURRENT_TIMESTAMP, "localtime")'
  
      def visit_true(self, expr, **kw):
          return '1'
  
      def visit_false(self, expr, **kw):
          return '0'
  
      def visit_char_length_func(self, fn, **kw):
          return "length%s" % self.function_argspec(fn)
  
      def visit_cast(self, cast, **kwargs):
          if self.dialect.supports_cast:
              return super(SQLiteCompiler, self).visit_cast(cast, **kwargs)
          else:
              return self.process(cast.clause, **kwargs)
  
      def visit_extract(self, extract, **kw):
          try:
              return "CAST(STRFTIME('%s', %s) AS INTEGER)" % (
                  self.extract_map[extract.field],
                  self.process(extract.expr, **kw)
              )
          except KeyError:
              raise exc.CompileError(
                  "%s is not a valid extract argument." % extract.field)
  
      def limit_clause(self, select):
          text = ""
          if select._limit is not None:
              text += "\n LIMIT " + self.process(sql.literal(select._limit))
          if select._offset is not None:
              if select._limit is None:
                  text += "\n LIMIT " + self.process(sql.literal(-1))
              text += " OFFSET " + self.process(sql.literal(select._offset))
          else:
              text += " OFFSET " + self.process(sql.literal(0))
          return text
  
      def for_update_clause(self, select):
          # sqlite has no "FOR UPDATE" AFAICT
          return ''
  
  
  class SQLiteDDLCompiler(compiler.DDLCompiler):
  
      def get_column_specification(self, column, **kwargs):
          coltype = self.dialect.type_compiler.process(column.type)
          colspec = self.preparer.format_column(column) + " " + coltype
          default = self.get_column_default_string(column)
          if default is not None:
              colspec += " DEFAULT " + default
  
          if not column.nullable:
              colspec += " NOT NULL"
  
          if (column.primary_key and
                  column.table.dialect_options['sqlite']['autoincrement'] and
                  len(column.table.primary_key.columns) == 1 and
                  issubclass(column.type._type_affinity, sqltypes.Integer) and
                  not column.foreign_keys):
              colspec += " PRIMARY KEY AUTOINCREMENT"
  
          return colspec
  
      def visit_primary_key_constraint(self, constraint):
          # for columns with sqlite_autoincrement=True,
          # the PRIMARY KEY constraint can only be inline
          # with the column itself.
          if len(constraint.columns) == 1:
              c = list(constraint)[0]
              if (c.primary_key and
                      c.table.dialect_options['sqlite']['autoincrement'] and
                      issubclass(c.type._type_affinity, sqltypes.Integer) and
                      not c.foreign_keys):
                  return None
  
          return super(SQLiteDDLCompiler, self).visit_primary_key_constraint(
              constraint)
  
      def visit_foreign_key_constraint(self, constraint):
  
          local_table = list(constraint._elements.values())[0].parent.table
          remote_table = list(constraint._elements.values())[0].column.table
  
          if local_table.schema != remote_table.schema:
              return None
          else:
              return super(
                  SQLiteDDLCompiler,
                  self).visit_foreign_key_constraint(constraint)
  
      def define_constraint_remote_table(self, constraint, table, preparer):
          """Format the remote table clause of a CREATE CONSTRAINT clause."""
  
          return preparer.format_table(table, use_schema=False)
  
      def visit_create_index(self, create):
          index = create.element
  
          text = super(SQLiteDDLCompiler, self).visit_create_index(
              create, include_table_schema=False)
  
          whereclause = index.dialect_options["sqlite"]["where"]
          if whereclause is not None:
              where_compiled = self.sql_compiler.process(
                  whereclause, include_table=False,
                  literal_binds=True)
              text += " WHERE " + where_compiled
  
          return text
  
  
  class SQLiteTypeCompiler(compiler.GenericTypeCompiler):
      def visit_large_binary(self, type_):
          return self.visit_BLOB(type_)
  
  
  class SQLiteIdentifierPreparer(compiler.IdentifierPreparer):
      reserved_words = set([
          'add', 'after', 'all', 'alter', 'analyze', 'and', 'as', 'asc',
          'attach', 'autoincrement', 'before', 'begin', 'between', 'by',
          'cascade', 'case', 'cast', 'check', 'collate', 'column', 'commit',
          'conflict', 'constraint', 'create', 'cross', 'current_date',
          'current_time', 'current_timestamp', 'database', 'default',
          'deferrable', 'deferred', 'delete', 'desc', 'detach', 'distinct',
          'drop', 'each', 'else', 'end', 'escape', 'except', 'exclusive',
          'explain', 'false', 'fail', 'for', 'foreign', 'from', 'full', 'glob',
          'group', 'having', 'if', 'ignore', 'immediate', 'in', 'index',
          'indexed', 'initially', 'inner', 'insert', 'instead', 'intersect',
          'into', 'is', 'isnull', 'join', 'key', 'left', 'like', 'limit',
          'match', 'natural', 'not', 'notnull', 'null', 'of', 'offset', 'on',
          'or', 'order', 'outer', 'plan', 'pragma', 'primary', 'query',
          'raise', 'references', 'reindex', 'rename', 'replace', 'restrict',
          'right', 'rollback', 'row', 'select', 'set', 'table', 'temp',
          'temporary', 'then', 'to', 'transaction', 'trigger', 'true', 'union',
          'unique', 'update', 'using', 'vacuum', 'values', 'view', 'virtual',
          'when', 'where',
      ])
  
      def format_index(self, index, use_schema=True, name=None):
          """Prepare a quoted index and schema name."""
  
          if name is None:
              name = index.name
          result = self.quote(name, index.quote)
          if (not self.omit_schema and
                  use_schema and
                  getattr(index.table, "schema", None)):
              result = self.quote_schema(
                  index.table.schema, index.table.quote_schema) + "." + result
          return result
  
  
  class SQLiteExecutionContext(default.DefaultExecutionContext):
      @util.memoized_property
      def _preserve_raw_colnames(self):
          return self.execution_options.get("sqlite_raw_colnames", False)
  
      def _translate_colname(self, colname):
          # adjust for dotted column names.  SQLite
          # in the case of UNION may store col names as
          # "tablename.colname", or if using an attached database,
          # "database.tablename.colname", in cursor.description
          if not self._preserve_raw_colnames and "." in colname:
              return colname.split(".")[-1], colname
          else:
              return colname, None
  
  
  class SQLiteDialect(default.DefaultDialect):
      name = 'sqlite'
      supports_alter = False
      supports_unicode_statements = True
      supports_unicode_binds = True
      supports_default_values = True
      supports_empty_insert = False
      supports_cast = True
      supports_multivalues_insert = True
      supports_right_nested_joins = False
  
      default_paramstyle = 'qmark'
      execution_ctx_cls = SQLiteExecutionContext
      statement_compiler = SQLiteCompiler
      ddl_compiler = SQLiteDDLCompiler
      type_compiler = SQLiteTypeCompiler
      preparer = SQLiteIdentifierPreparer
      ischema_names = ischema_names
      colspecs = colspecs
      isolation_level = None
  
      supports_cast = True
      supports_default_values = True
  
      construct_arguments = [
          (sa_schema.Table, {
              "autoincrement": False
          }),
          (sa_schema.Index, {
              "where": None,
          }),
      ]
  
      _broken_fk_pragma_quotes = False
  
      def __init__(self, isolation_level=None, native_datetime=False, **kwargs):
          default.DefaultDialect.__init__(self, **kwargs)
          self.isolation_level = isolation_level
  
          # this flag used by pysqlite dialect, and perhaps others in the
          # future, to indicate the driver is handling date/timestamp
          # conversions (and perhaps datetime/time as well on some hypothetical
          # driver ?)
          self.native_datetime = native_datetime
  
          if self.dbapi is not None:
              self.supports_default_values = (
                  self.dbapi.sqlite_version_info >= (3, 3, 8))
              self.supports_cast = (
                  self.dbapi.sqlite_version_info >= (3, 2, 3))
              self.supports_multivalues_insert = (
                  # http://www.sqlite.org/releaselog/3_7_11.html
                  self.dbapi.sqlite_version_info >= (3, 7, 11))
              # see http://www.sqlalchemy.org/trac/ticket/2568
              # as well as http://www.sqlite.org/src/info/600482d161
              self._broken_fk_pragma_quotes = (
                  self.dbapi.sqlite_version_info < (3, 6, 14))
  
      _isolation_lookup = {
          'READ UNCOMMITTED': 1,
          'SERIALIZABLE': 0,
      }
  
      def set_isolation_level(self, connection, level):
          try:
              isolation_level = self._isolation_lookup[level.replace('_', ' ')]
          except KeyError:
              raise exc.ArgumentError(
                  "Invalid value '%s' for isolation_level. "
                  "Valid isolation levels for %s are %s" %
                  (level, self.name, ", ".join(self._isolation_lookup))
              )
          cursor = connection.cursor()
          cursor.execute("PRAGMA read_uncommitted = %d" % isolation_level)
          cursor.close()
  
      def get_isolation_level(self, connection):
          cursor = connection.cursor()
          cursor.execute('PRAGMA read_uncommitted')
          res = cursor.fetchone()
          if res:
              value = res[0]
          else:
              # http://www.sqlite.org/changes.html#version_3_3_3
              # "Optional READ UNCOMMITTED isolation (instead of the
              # default isolation level of SERIALIZABLE) and
              # table level locking when database connections
              # share a common cache.""
              # pre-SQLite 3.3.0 default to 0
              value = 0
          cursor.close()
          if value == 0:
              return "SERIALIZABLE"
          elif value == 1:
              return "READ UNCOMMITTED"
          else:
              assert False, "Unknown isolation level %s" % value
  
      def on_connect(self):
          if self.isolation_level is not None:
              def connect(conn):
                  self.set_isolation_level(conn, self.isolation_level)
              return connect
          else:
              return None
  
      @reflection.cache
      def get_table_names(self, connection, schema=None, **kw):
          if schema is not None:
              qschema = self.identifier_preparer.quote_identifier(schema)
              master = '%s.sqlite_master' % qschema
              s = ("SELECT name FROM %s "
                   "WHERE type='table' ORDER BY name") % (master,)
              rs = connection.execute(s)
          else:
              try:
                  s = ("SELECT name FROM "
                       " (SELECT * FROM sqlite_master UNION ALL "
                       "  SELECT * FROM sqlite_temp_master) "
                       "WHERE type='table' ORDER BY name")
                  rs = connection.execute(s)
              except exc.DBAPIError:
                  s = ("SELECT name FROM sqlite_master "
                       "WHERE type='table' ORDER BY name")
                  rs = connection.execute(s)
  
          return [row[0] for row in rs]
  
      def has_table(self, connection, table_name, schema=None):
          quote = self.identifier_preparer.quote_identifier
          if schema is not None:
              pragma = "PRAGMA %s." % quote(schema)
          else:
              pragma = "PRAGMA "
          qtable = quote(table_name)
          statement = "%stable_info(%s)" % (pragma, qtable)
          cursor = _pragma_cursor(connection.execute(statement))
          row = cursor.fetchone()
  
          # consume remaining rows, to work around
          # http://www.sqlite.org/cvstrac/tktview?tn=1884
          while not cursor.closed and cursor.fetchone() is not None:
              pass
  
          return row is not None
  
      @reflection.cache
      def get_view_names(self, connection, schema=None, **kw):
          if schema is not None:
              qschema = self.identifier_preparer.quote_identifier(schema)
              master = '%s.sqlite_master' % qschema
              s = ("SELECT name FROM %s "
                   "WHERE type='view' ORDER BY name") % (master,)
              rs = connection.execute(s)
          else:
              try:
                  s = ("SELECT name FROM "
                       " (SELECT * FROM sqlite_master UNION ALL "
                       "  SELECT * FROM sqlite_temp_master) "
                       "WHERE type='view' ORDER BY name")
                  rs = connection.execute(s)
              except exc.DBAPIError:
                  s = ("SELECT name FROM sqlite_master "
                       "WHERE type='view' ORDER BY name")
                  rs = connection.execute(s)
  
          return [row[0] for row in rs]
  
      @reflection.cache
      def get_view_definition(self, connection, view_name, schema=None, **kw):
          if schema is not None:
              qschema = self.identifier_preparer.quote_identifier(schema)
              master = '%s.sqlite_master' % qschema
              s = ("SELECT sql FROM %s WHERE name = '%s'"
                   "AND type='view'") % (master, view_name)
              rs = connection.execute(s)
          else:
              try:
                  s = ("SELECT sql FROM "
                       " (SELECT * FROM sqlite_master UNION ALL "
                       "  SELECT * FROM sqlite_temp_master) "
                       "WHERE name = '%s' "
                       "AND type='view'") % view_name
                  rs = connection.execute(s)
              except exc.DBAPIError:
                  s = ("SELECT sql FROM sqlite_master WHERE name = '%s' "
                       "AND type='view'") % view_name
                  rs = connection.execute(s)
  
          result = rs.fetchall()
          if result:
              return result[0].sql
  
      @reflection.cache
      def get_columns(self, connection, table_name, schema=None, **kw):
          quote = self.identifier_preparer.quote_identifier
          if schema is not None:
              pragma = "PRAGMA %s." % quote(schema)
          else:
              pragma = "PRAGMA "
          qtable = quote(table_name)
          statement = "%stable_info(%s)" % (pragma, qtable)
          c = _pragma_cursor(connection.execute(statement))
  
          rows = c.fetchall()
          columns = []
          for row in rows:
              (name, type_, nullable, default, primary_key) = (
                  row[1], row[2].upper(), not row[3], row[4], row[5])
  
              columns.append(self._get_column_info(name, type_, nullable,
                                                   default, primary_key))
          return columns
  
      def _get_column_info(self, name, type_, nullable, default, primary_key):
          coltype = self._resolve_type_affinity(type_)
  
          if default is not None:
              default = util.text_type(default)
  
          return {
              'name': name,
              'type': coltype,
              'nullable': nullable,
              'default': default,
              'autoincrement': default is None,
              'primary_key': primary_key,
          }
  
      def _resolve_type_affinity(self, type_):
          """Return a data type from a reflected column, using affinity tules.
  
          SQLite's goal for universal compatibility introduces some complexity
          during reflection, as a column's defined type might not actually be a
          type that SQLite understands - or indeed, my not be defined *at all*.
          Internally, SQLite handles this with a 'data type affinity' for each
          column definition, mapping to one of 'TEXT', 'NUMERIC', 'INTEGER',
          'REAL', or 'NONE' (raw bits). The algorithm that determines this is
          listed in http://www.sqlite.org/datatype3.html section 2.1.
  
          This method allows SQLAlchemy to support that algorithm, while still
          providing access to smarter reflection utilities by regcognizing
          column definitions that SQLite only supports through affinity (like
          DATE and DOUBLE).
  
          """
          match = re.match(r'([\w ]+)(\(.*?\))?', type_)
          if match:
              coltype = match.group(1)
              args = match.group(2)
          else:
              coltype = ''
              args = ''
  
          if coltype in self.ischema_names:
              coltype = self.ischema_names[coltype]
          elif 'INT' in coltype:
              coltype = sqltypes.INTEGER
          elif 'CHAR' in coltype or 'CLOB' in coltype or 'TEXT' in coltype:
              coltype = sqltypes.TEXT
          elif 'BLOB' in coltype or not coltype:
              coltype = sqltypes.NullType
          elif 'REAL' in coltype or 'FLOA' in coltype or 'DOUB' in coltype:
              coltype = sqltypes.REAL
          else:
              coltype = sqltypes.NUMERIC
  
          if args is not None:
              args = re.findall(r'(\d+)', args)
              try:
                  coltype = coltype(*[int(a) for a in args])
              except TypeError:
                  util.warn(
                      "Could not instantiate type %s with "
                      "reflected arguments %s; using no arguments." %
                      (coltype, args))
                  coltype = coltype()
          else:
              coltype = coltype()
  
          return coltype
  
      @reflection.cache
      def get_pk_constraint(self, connection, table_name, schema=None, **kw):
          cols = self.get_columns(connection, table_name, schema, **kw)
          pkeys = []
          for col in cols:
              if col['primary_key']:
                  pkeys.append(col['name'])
          return {'constrained_columns': pkeys, 'name': None}
  
      @reflection.cache
      def get_foreign_keys(self, connection, table_name, schema=None, **kw):
          quote = self.identifier_preparer.quote_identifier
          if schema is not None:
              pragma = "PRAGMA %s." % quote(schema)
          else:
              pragma = "PRAGMA "
          qtable = quote(table_name)
          statement = "%sforeign_key_list(%s)" % (pragma, qtable)
          c = _pragma_cursor(connection.execute(statement))
          fkeys = []
          fks = {}
          while True:
              row = c.fetchone()
              if row is None:
                  break
              (numerical_id, rtbl, lcol, rcol) = (
                  row[0], row[2], row[3], row[4])
  
              self._parse_fk(fks, fkeys, numerical_id, rtbl, lcol, rcol)
          return fkeys
  
      def _parse_fk(self, fks, fkeys, numerical_id, rtbl, lcol, rcol):
          # sqlite won't return rcol if the table was created with REFERENCES
          # <tablename>, no col
          if rcol is None:
              rcol = lcol
  
          if self._broken_fk_pragma_quotes:
              rtbl = re.sub(r'^[\"\[`\']|[\"\]`\']$', '', rtbl)
  
          try:
              fk = fks[numerical_id]
          except KeyError:
              fk = {
                  'name': None,
                  'constrained_columns': [],
                  'referred_schema': None,
                  'referred_table': rtbl,
                  'referred_columns': [],
              }
              fkeys.append(fk)
              fks[numerical_id] = fk
  
          if lcol not in fk['constrained_columns']:
              fk['constrained_columns'].append(lcol)
          if rcol not in fk['referred_columns']:
              fk['referred_columns'].append(rcol)
          return fk
  
      @reflection.cache
      def get_indexes(self, connection, table_name, schema=None, **kw):
          quote = self.identifier_preparer.quote_identifier
          if schema is not None:
              pragma = "PRAGMA %s." % quote(schema)
          else:
              pragma = "PRAGMA "
          include_auto_indexes = kw.pop('include_auto_indexes', False)
          qtable = quote(table_name)
          statement = "%sindex_list(%s)" % (pragma, qtable)
          c = _pragma_cursor(connection.execute(statement))
          indexes = []
          while True:
              row = c.fetchone()
              if row is None:
                  break
              # ignore implicit primary key index.
              # http://www.mail-archive.com/sqlite-users@sqlite.org/msg30517.html
              elif (not include_auto_indexes and
                    row[1].startswith('sqlite_autoindex')):
                  continue
  
              indexes.append(dict(name=row[1], column_names=[], unique=row[2]))
          # loop thru unique indexes to get the column names.
          for idx in indexes:
              statement = "%sindex_info(%s)" % (pragma, quote(idx['name']))
              c = connection.execute(statement)
              cols = idx['column_names']
              while True:
                  row = c.fetchone()
                  if row is None:
                      break
                  cols.append(row[2])
          return indexes
  
      @reflection.cache
      def get_unique_constraints(self, connection, table_name,
                                 schema=None, **kw):
          UNIQUE_SQL = """
              SELECT sql
              FROM
                  sqlite_master
              WHERE
                  type='table' AND
                  name=:table_name
          """
          c = connection.execute(UNIQUE_SQL, table_name=table_name)
          table_data = c.fetchone()[0]
  
          UNIQUE_PATTERN = 'CONSTRAINT (\w+) UNIQUE \(([^\)]+)\)'
          return [
              {'name': name,
               'column_names': [col.strip(' "') for col in cols.split(',')]}
              for name, cols in re.findall(UNIQUE_PATTERN, table_data)
          ]
  
  
  def _pragma_cursor(cursor):
      """work around SQLite issue whereby cursor.description
      is blank when PRAGMA returns no rows."""
  
      if cursor.closed:
          cursor.fetchone = lambda: None
          cursor.fetchall = lambda: []
      return cursor
  