Virtual Serial Device in Python?

Question

I know that I can use e.g. pySerial to talk to serial devices, but what if I don't have a device right now but still need to write a client for it? How can I write a "virtual serial device" in Python and have pySerial talk to it, like I would, say, run a local web server? Maybe I'm just not searching well, but I've been unable to find any information on this topic.

Answer 1

this is something I did and worked out for me so far:

import os, pty, serial  master, slave = pty.openpty() s_name = os.ttyname(slave)  ser = serial.Serial(s_name)  # To Write to the device ser.write('Your text')  # To read from the device os.read(master,1000) 

If you create more virtual ports you will have no problems as the different masters get different file descriptors even if they have the same name.

Answer 2

I was able to emulate an arbitrary serial port ./foo using this code:

SerialEmulator.py

import os, subprocess, serial, time  # this script lets you emulate a serial device # the client program should use the serial port file specifed by client_port  # if the port is a location that the user can't access (ex: /dev/ttyUSB0 often), # sudo is required  class SerialEmulator(object):     def __init__(self, device_port='./ttydevice', client_port='./ttyclient'):         self.device_port = device_port         self.client_port = client_port         cmd=['/usr/bin/socat','-d','-d','PTY,link=%s,raw,echo=0' %                 self.device_port, 'PTY,link=%s,raw,echo=0' % self.client_port]         self.proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)         time.sleep(1)         self.serial = serial.Serial(self.device_port, 9600, rtscts=True, dsrdtr=True)         self.err = ''         self.out = ''      def write(self, out):         self.serial.write(out)      def read(self):         line = ''         while self.serial.inWaiting() > 0:             line += self.serial.read(1)         print line      def __del__(self):         self.stop()      def stop(self):         self.proc.kill()         self.out, self.err = self.proc.communicate() 

socat needs to be installed (sudo apt-get install socat), as well as the pyserial python package (pip install pyserial).

Open the python interpreter and import SerialEmulator:

>>> from SerialEmulator import SerialEmulator >>> emulator = SerialEmulator('./ttydevice','./ttyclient')  >>> emulator.write('foo') >>> emulator.read() 

Your client program can then wrap ./ttyclient with pyserial, creating the virtual serial port. You could also make client_port /dev/ttyUSB0 or similar if you can't modify client code, but might need sudo.

Also be aware of this issue: Pyserial does not play well with virtual port