PySerial write() instant timeout

Question

EDIT I found out what the problem was and have answered my own question. Original question below this line I have a serial bridge between `COM4` and `COM5` implemented in software (Specifically, HDD's Free Virtual Serial Configuration Utility) I have two different python scripts starting up in two different instances of Powershell, receive first: ``` import serial receive = serial.Serial(port = 'COM5', baudrate = 9600) text = receive.read(100) receive.close() print text ``` And then the sender: ``` import serial send = serial.Serial(port = 'COM4', baudrate = 9600, timeout = 0) send.write("Hello") send.close() ``` When starting the sender script, the receiver script gets the sent message (So communication is clearly established) but the sender script immediately ends with an error: ``` Traceback (most recent call last): File ".\sending.py", line 3, in <module> send.writelines("Hello") File "C:\Python27\lib\site-packages\serial\serialwin32.py", line 270, in write raise writeTimeoutError…

Accepted Answer

The clue is in the error message[1]

```
File "C:\Python27\lib\site-packages\serial\serialwin32.py", line 270, in write
raise writeTimeoutError
```

so we open that file and find:

```
if self._writeTimeout != 0: # if blocking (None) or w/ write timeout (>0)
            # Wait for the write to complete.
            #~ win32.WaitForSingleObject(self._overlappedWrite.hEvent, win32.INFINITE)
            err = win32.GetOverlappedResult(self.hComPort, self._overlappedWrite, ctypes.byref(n), True)
            if n.value != len(data):
                raise writeTimeoutError
```

Read that first conditional again:

```
if self._writeTimeout != 0:
```

so let us rewrite our code from before

```
send = serial.Serial(port = 'COM4', baudrate = 9600, timeout = 0)
```

becomes

```
send = serial.Serial(port = 'COM4', baudrate = 9600, writeTimeout = 0)
```

and Et Voila: No exception.

[1] Well Designed Error Messages? That's new!

PySerial write() instant timeout

Solution

Problem