Reading Stdout From Xinput Test In Python

I am trying to stream the output of xinput into my python program, however my program just waits and stays blank. I think it may have something to do with buffering but I cannot sa

Solution 1:

Your code works for me; however it looks like the xinput cmd buffers its output if not connected to a tty. When running your code, keep moving the mouse and eventually xinput should flush stdout and you'll see your lines show up in chunks... at least i did when running your code.

I re-wrote your code to eliminate buffering, but I couldn't get it to not come out in chunks, hence why I believe xinput is to blame. When not connected to a TTY, it doesn't flush the stdout buffer with each new event. This can be verified with xinput test 15 | cat. Moving your mouse will cause the data to print in buffered chunks; just like your code.

My test code is below if helpful

#!/usr/bin/python -u

# the -u flag makes python not buffer stdios


import os
from subprocess import Popen

_read, _write = os.pipe()

# I tried os.fork() to see if buffering was happening
# in subprocess, but it isn't

#if not os.fork():
#    os.close(_read)
#    os.close(1) # stdout
#    os.dup2(_write, 1)
#
#    os.execlp('xinput', 'xinput', 'test', '11')
#    os._exit(0) # Should never get eval'd

write_fd = os.fdopen(_write, 'w', 0)
proc = Popen(['xinput', 'test', '11'], stdout = write_fd)

os.close(_write)

# when using os.read() there is no readline method
# i made a generator
def read_line():
    line = []
    while True:
        c = os.read(_read, 1)
        if not c: raise StopIteration
        if c == '\n':
            yield "".join(line)
            line = []
            continue
        line += c



readline = read_line()

for each in readline:
    print each

Solution 2:

Take a look at sh, specifically this tutorial http://amoffat.github.com/sh/tutorials/1-real_time_output.html

import sh
for line in sh.xinput("test", mouse_id, _iter=True):
    print(line)