Writing to a serial port

Question

Using serial library on Windows.

I open a serial port successfully and then do a write() and it's never returning.

There is nothing on the other side reading the port

        s = serial.Serial()
        s.port = "COM3:"
        #s.timeout = 0.05
        #s.baudrate = 115200
        #s.parity =  serial.PARITY_NONE
        s.open()
        assert s.is_open

        print("A")
        s.write("XXX".encode())
        print("B")  # don't see this

The above code works once.

The second time it hangs on the write()