def error_message(self):
        "Returns a one-line description of the error."
        output = self.msg + ", code " + str(self.code)
        output += ". Request Time={}, Request ID={}".format(self.timestamp, self.req_id)
        if self.name != self.__class__.__name__:
            output = self.name + ": " + output
        return output
Returns a one-line description of the error.