def _to_string(self):
        """
        Return a string representing this location.
        unicode(self) returns something like this: "519665f6223ebd6980884f2b+type+problem"
        """
        return u"{}+{}@{}".format(text_type(self.definition_id), self.BLOCK_TYPE_PREFIX, self.block_type)
Return a string representing this location.
        unicode(self) returns something like this: "519665f6223ebd6980884f2b+type+problem"