Tries to get the mapper from a row instance.
    http://docs.sqlalchemy.org/en/latest/orm/tutorial.html#declare-a-mapping

    :param row: instance of the declarative base class

    :return: instance of :class:`sqlalchemy.orm.mapper.Mapper`

def get_mapper(row):
    """
    Tries to get the mapper from a row instance.
    http://docs.sqlalchemy.org/en/latest/orm/tutorial.html#declare-a-mapping

    :param row: instance of the declarative base class

    :return: instance of :class:`sqlalchemy.orm.mapper.Mapper`
    """
    try:
        mapper = getattr(row, '__mapper__')
    except AttributeError as e:
        e.args = ('Row must be instance of the declarative base class, '
                  'got %s instead' % type(row).__name__,)
        raise

    return mapper