Just to be clear, the issue is not in Python: the deadlock will happen if you won't consume the pipe whatever language you use to spawn a subprocess -- the buff

Just to be clear, the issue is not in Python: the deadlock will happen if you won't consume the pipe whatever language you use to spawn a subprocess -- the buffer is not in your application -- it is the OS pipe buffer. I imagine your broken code did something like: #XXX WRONG, DON'T DO IT p = Popen(cmd, stdout=PIPE) p.wait() #XXX deadlock is possible if cmd generates enough output output = p.stdout.read() To avoid the deadlock, it is enough to swap the last two statements: p = Popen(cmd, stdout=PIPE) output = p.stdout.read() p.wait() that you would normally write as: output = check_output(cmd) # 2.7+ If you need to consume more than one pipe separately then you should consume them concurrently and therefore you need threads or async.io. `Popen.communicate()` can read from both pipes concurrently (as you've mentioned) and it is always available. It was available even in Python 2.4 that introduced the subprocess module.