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POPython subprocess question
 

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    <p>I would like to be able to spawn a process in python and have two way communication. Of course, Pexpect does this and is indeed a way I might go. However, it is not quite ideal.</p> <p>My ideal situation would be to have a cross platform generic technique that involved only the standard python libraries. Subprocess gets pretty close, but the fact that I have to wait for the process to terminate before safely interacting with it is not desirable.</p> <p>Looking at the documentation, it does say there is a stdin,stdout and stderr file descriptors that I can directly manipulate, but there is a big fat warning that says "Don't Do This". Unfortunately its not entirely clear why this warning exists, but from what I gather from google is that it is related to os buffering, and it is possible to write code that unexpectedly deadlocks when those internal buffers fail (as a side note, any examples that show the wrong way and right way would be appreciated).</p> <p>So, risking my code to potential deadlocks, I thought it might be interesting to use poll or select to interactively read from the running process without killing it. Although I lose (i think) the cross platform ability, I like the fact that it requires no additional libraries. But more importantly, I would like to know if this is this a good idea. I have yet to try this approach, but I am concerned about gotchas that could potentially devastate my program. Can it work? What should I test for?</p> <p>In my specific case I am not really concerned about being able to write to the process, just repeatedly reading from it. Also, I don't expect my processes to dump huge amounts of text, so I hope to avoid the deadlocking issue, however I would like to know exactly what those limits are and be able to write some tests to see where it breaks down.</p>
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    1. COArgh! All my hopes and dreams appeared to be crushed by stdout buffering! Why wont the operating system just give me those bits :<
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    2. COare you calling some external third party tools that Python doesn't have a module/library for?
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    3. COIn a way, yes. Luckily, those happen to be in my control, so I have some flexibility in my solution. If the called script flushes stdout, then I can work with it interactively. Ideally, I wish I could make stdout an unbuffered stream, but that appears to be impossible.
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