def __init__(self, to, **kwargs):
        try:
            assert not to._meta.abstract, "%s cannot define a relation with abstract class %s" % (self.__class__.__name__, to._meta.object_name)
        except AttributeError:  # to._meta doesn't exist, so it must be RECURSIVE_RELATIONSHIP_CONSTANT
            assert isinstance(to, six.string_types), "%s(%r) is invalid. First parameter to ManyToManyField must be either a model, a model name, or the string %r" % (self.__class__.__name__, to, RECURSIVE_RELATIONSHIP_CONSTANT)
            # Python 2.6 and earlier require dictionary keys to be of str type,
            # not unicode and class names must be ASCII (in Python 2.x), so we
            # forcibly coerce it here (breaks early if there's a problem).
            to = str(to)

        kwargs['verbose_name'] = kwargs.get('verbose_name', None)
        kwargs['rel'] = ManyToManyRel(to,
            related_name=kwargs.pop('related_name', None),
            limit_choices_to=kwargs.pop('limit_choices_to', None),
            symmetrical=kwargs.pop('symmetrical', to == RECURSIVE_RELATIONSHIP_CONSTANT),
            through=kwargs.pop('through', None))

        self.db_table = kwargs.pop('db_table', None)
        if kwargs['rel'].through is not None:
            assert self.db_table is None, "Cannot specify a db_table if an intermediary model is used."

        Field.__init__(self, **kwargs)

        msg = _('Hold down "Control", or "Command" on a Mac, to select more than one.')
        self.help_text = string_concat(self.help_text, ' ', msg)
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.5/django/db/models/fields/related.py/ManyToManyField.__init__/original