Returns ``True`` if field has changed from currently saved value

def has_changed(self, field):
        """Returns ``True`` if field has changed from currently saved value"""
        if not self.instance.pk:
            return True
        elif field in self.saved_data:
            return self.previous(field) != self.get_field_value(field)
        else:
            raise FieldError('field "%s" not tracked' % field)