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 field in self.fields:
            # deferred fields haven't changed
            if field in self.deferred_fields and field not in self.instance.__dict__:
                return False
            return self.previous(field) != self.get_field_value(field)
        else:
            raise FieldError('field "%s" not tracked' % field)