'Validates that the input is a list or tuple.'

def validate(self, value):

    if (self.required and (not value)):
        raise ValidationError(self.error_messages[u'required'], code=u'required')
    for val in value:
        if (not self.valid_value(val)):
            raise ValidationError(self.error_messages[u'invalid_choice'], code=u'invalid_choice', params={u'value': val})
