from sqlalchemy.orm import sessionmaker

class WithSession(object):

    '''a with statement for a database session connection.'''

    def __init__(self, engine, autocommit=False):

        """

        :param `sqlalchemy.engine.base.Engine` engine: a valid sqlalchemy engine object (normally created via :func:`sqlalchemy.create_engine`).

        :param boolean autocommit: autocommit after running the function.

        .. automethod:: __enter__

        """

        self.engine = engine

        self.autocommit=autocommit

    def __enter__(self):

        """returns a vaild session object"""

        self.session = sessionmaker(bind=self.engine)()

        return self.session

    def __exit__(self,exc_type, exc_value, traceback):

        if exc_type is None:

            if self.autocommit:

                self.session.commit()

        else:

            self.session.rollback()

        self.session.close()