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I think you may be examining the wrong problem. Certainly as Aaron says if you try to be both a producer to the beginning of a pipeline, and a consumer of the end of the pipeline, it is easy to get into a deadlock situation. This is the problem that communicate() solves. communicate() isn't exactly correct for you since stdin and stdout are on different subprocess objects; but if you take a look at the implementation in subprocess.py you'll see that it does exactly what Aaron suggested. Once you see that communicate both reads and writes, you'll see that in your second try communicate() competes with p2 for the output of p1: <pre><code>p1 = Popen(["grep", "-v", "not"], stdin=PIPE, stdout=PIPE) p2 = Popen(["cut", "-c", "1-10"], stdin=p1.stdout, stdout=PIPE) # ... p1.communicate('data\n') # reads from p1.stdout, as does p2 </code></pre> I am running on win32, which definitely has different i/o and buffering characteristics, but this works for me: <pre><code>p1 = Popen(["grep", "-v", "not"], stdin=PIPE, stdout=PIPE) p2 = Popen(["cut", "-c", "1-10"], stdin=p1.stdout, stdout=PIPE) t = threading.Thread(target=get_output, args=(p2,)) t.start() p1.stdin.write('hello world\n' * 100000) p1.stdin.close() t.join() </code></pre> I tuned the input size to produce a deadlock when using a naive unthreaded p2.read() You might also try buffering into a file, eg <pre><code>fd, _ = tempfile.mkstemp() os.write(fd, 'hello world\r\n' * 100000) os.lseek(fd, 0, os.SEEK_SET) p1 = Popen(["grep", "-v", "not"], stdin=fd, stdout=PIPE) p2 = Popen(["cut", "-c", "1-10"], stdin=p1.stdout, stdout=PIPE) print p2.stdout.read() </code></pre> That also works for me without deadlocks.
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1. POblocks - send input to python subprocess pipeline
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1. USPaul Du Bois
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1. COThanks!!! I checked `subprocess.py` and tried to do as you said, but it still blocks. I've updated my question. HELP!!!
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