def write(self, datagram, addr=None):
        """
        Write a datagram.

        @type datagram: L{bytes}
        @param datagram: The datagram to be sent.

        @type addr: L{tuple} containing L{str} as first element and L{int} as
            second element, or L{None}
        @param addr: A tuple of (I{stringified IPv4 or IPv6 address},
            I{integer port number}); can be L{None} in connected mode.
        """
        if self._connectedAddr:
            assert addr in (None, self._connectedAddr)
            try:
                return self.socket.send(datagram)
            except socket.error as se:
                no = se.args[0]
                if no == EINTR:
                    return self.write(datagram)
                elif no == EMSGSIZE:
                    raise error.MessageLengthError("message too long")
                elif no == ECONNREFUSED:
                    self.protocol.connectionRefused()
                else:
                    raise
        else:
            assert addr != None
            if (not abstract.isIPAddress(addr[0])
                    and not abstract.isIPv6Address(addr[0])
                    and addr[0] != "<broadcast>"):
                raise error.InvalidAddressError(
                    addr[0],
                    "write() only accepts IP addresses, not hostnames")
            if ((abstract.isIPAddress(addr[0]) or addr[0] == "<broadcast>")
                    and self.addressFamily == socket.AF_INET6):
                raise error.InvalidAddressError(
                    addr[0],
                    "IPv6 port write() called with IPv4 or broadcast address")
            if (abstract.isIPv6Address(addr[0])
                    and self.addressFamily == socket.AF_INET):
                raise error.InvalidAddressError(
                    addr[0], "IPv4 port write() called with IPv6 address")
            try:
                return self.socket.sendto(datagram, addr)
            except socket.error as se:
                no = se.args[0]
                if no == EINTR:
                    return self.write(datagram, addr)
                elif no == EMSGSIZE:
                    raise error.MessageLengthError("message too long")
                elif no == ECONNREFUSED:
                    # in non-connected UDP ECONNREFUSED is platform dependent, I
                    # think and the info is not necessarily useful. Nevertheless
                    # maybe we should call connectionRefused? XXX
                    return
                else:
                    raise

        Write a datagram.

        @type datagram: L{bytes}
        @param datagram: The datagram to be sent.

        @type addr: L{tuple} containing L{str} as first element and L{int} as
            second element, or L{None}
        @param addr: A tuple of (I{stringified IPv4 or IPv6 address},
            I{integer port number}); can be L{None} in connected mode.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/udp.py