add attr to fields

def add_attr2fields(self, attr_name, attr_val, fields=[], exclude=[], include_all_if_empty=True):
        """
        add attr to fields
        """
        for f in self.filter_fields(fields, exclude, include_all_if_empty):
            f = self.fields[f.name]
            org_val = f.widget.attrs.get(attr_name, '')
            f.widget.attrs[attr_name] = '%s %s' % (org_val, attr_val) if org_val else attr_val