def recvfrom(self, size):
        """
        Return (or raise) the next value from C{self.retvals}.
        """
        ret = self.retvals.pop(0)
        if isinstance(ret, socket.error):
            raise ret
        return ret, None

        Return (or raise) the next value from C{self.retvals}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_udp_internals.py