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POReading stderr of subprocess while it is executing
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2013-03-10T21:21:41.447
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I'd like to read what is written to stderr by a subprocess while it is executing. However, when I use this script that I've written, stderr does not seem to have anything for me to read until the subprocess has exited. <pre><code>#!/usr/bin/env python2 import sys from subprocess import Popen, PIPE, STDOUT if len(sys.argv) < 2: print "Please provide a command" sys.exit(1) sub = Popen(sys.argv[1:], stdout=PIPE, stderr=STDOUT) for i, line in enumerate(sub.stdout): sys.stdout.write("%d: %s" % (i, line)) </code></pre> edit: Ok, I've gotten closer now. If I specify the number of bytes to read it overcomes the buffering. <pre><code>#!/usr/bin/env python2 import sys from subprocess import Popen, PIPE, STDOUT if len(sys.argv) < 2: print "Please provide a command" sys.exit(1) sub = Popen(sys.argv[1:], stdout=PIPE, stderr=STDOUT) i = 0 while sub.poll() is None: line = sub.stdout.read(64) line.strip("\b") sys.stdout.write("%d: %s\n" % (i, line)) i += 1 </code></pre> Snippet of output: <pre class="lang-none prettyprint-override"><code>58: 86 q=21.0 size= 4541841kB time=00:00:22.08 bitrate=1685014.2kbi frame= 567 fps= 86 q=22.0 size= 4543667kB time=00:00:2 frame= 621 fps= 87 q=20.0 sizs/s frame= 4545352kB time=00:00:26.11 bitrate=1425939.2kbits/s 62: = 686 fps= 90 q=12.0 size= 4546970kB time=00:00:28.89 bitrate=1 frame= 758 fps= 93 q=25.0 size= 4548534kB t frame= 794 fps= 92 bitrate=1168185.5kbits/s 65: q=27.0 size= 4550901kB time=00:00:33.40 bitrate=1115897.0kbits/ frame= 827 fps= 91 q=27.0 size= 4552324kB time=00:00:34.7 frame= 857 fps= 89 q=26.0 size= frame= 254kB time=00:00:36.12 bitrate=1032874.9kbits/s 69: 892 fps= 88 q=25.0 size= 4556598kB time=00:00:37.36 bitrate=9988 frame= 948 fps= 89 q=19.0 size= 4558565kB time= frame= 1006 fps= 90 q=19937320.4kbits/s 72: .0 size= 4560139kB time=00:00:42.16 bitrate=885880.0kbits/s 73: frame= 1060 fps= 91 q=19.0 size= 4561958kB time=00:00:44.49 bitr frame= 1122 fps= 93 q=18.0 size= 4563460 frame= 1173 fps=0:47.08 bitrate=793898.4kbits/s </code></pre> It looks like my problem now is that ffmpeg is using backspace characters or similar to mess with stdout. Not sure what's happening here.
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<python><buffer><subprocess><stderr>
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Reading stderr of subprocess while it is executing
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