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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def init(uri=None, alembic_ini=None, engine=None, create=False):
 """ Initialize a connection. Create tables if requested."""


    if uri and engine:
        raise ValueError("uri and engine cannot both be specified")

    if uri is None and not engine:
        uri = 'sqlite:////tmp/datanommer.db'
        log.warning("No db uri given.  Using %r" % uri)

    if uri and not engine:
        engine = create_engine(uri)

    if 'sqlite' in engine.driver:
        # Enable nested transaction support under SQLite
        # See https://stackoverflow.com/questions/1654857/nested-transactions-with-sqlalchemy-and-sqlite
        @event.listens_for(engine, "connect")
        def do_connect(dbapi_connection, connection_record):
            # disable pysqlite's emitting of the BEGIN statement entirely.
            # also stops it from emitting COMMIT before any DDL.
            dbapi_connection.isolation_level = None

        @event.listens_for(engine, "begin")
        def do_begin(conn):
            # emit our own BEGIN
            conn.execute("BEGIN")

    # We need to hang our own attribute on the sqlalchemy session to stop
    # ourselves from initializing twice.  That is only a problem is the code
    # calling us isn't consistent.
    if getattr(session, '_datanommer_initialized', None):
        log.warning("Session already initialized.  Bailing")
        return
    session._datanommer_initialized = True

    session.configure(bind=engine)
    DeclarativeBase.query = session.query_property()

    # Loads the alembic configuration and generates the version table, with
    # the most recent revision stamped as head
    if alembic_ini is not None:
        from alembic.config import Config
        from alembic import command
        alembic_cfg = Config(alembic_ini)
        command.stamp(alembic_cfg, "head")

    if create:
        DeclarativeBase.metadata.create_all(engine)