[issue7678] subprocess.Popen pipeline example code in the documentation is lacking
Gregory P. Smith g...@krypto.org added the comment: documentation updated in r88352. thanks! -- assignee: docs@python - gregory.p.smith resolution: - fixed status: open - closed ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7678 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7678] subprocess.Popen pipeline example code in the documentation is lacking
Ross Lagerwall rosslagerw...@gmail.com added the comment: The docs should be updated. This has been noted in msg54949 and http://www.enricozini.org/2009/debian/python-pipes/ Perhaps this example will make it clear: import subprocess p1 = subprocess.Popen([yes], stdout=subprocess.PIPE) p2 = subprocess.Popen([head], stdin=p1.stdout, stdout=subprocess.PIPE) #p1.stdout.close() p1.wait() This example hangs. yes writes to head and head reads the first 10 lines and then exits. But, yes does not receive a SIGPIPE because the python process still has a p1.stdout open. Thus, p1.stdout should be closed after being passed to p2. -- nosy: +rosslagerwall ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7678 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7678] subprocess.Popen pipeline example code in the documentation is lacking
Éric Araujo mer...@netwok.org added the comment: As a non-expert user of subprocess, calling close before communicate seems strange to me. Does the example code with a bug work if close is called after communicate? In the 3.2 docs, we could update the example to use a with statement, unless it is deemed a distraction for this simple introductory section. -- nosy: +eric.araujo, gregory.p.smith -georg.brandl stage: - needs patch type: - behavior versions: +Python 2.7, Python 3.1, Python 3.2 -Python 2.6 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7678 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7678] subprocess.Popen pipeline example code in the documentation is lacking
Changes by Mark Lawrence breamore...@yahoo.co.uk: -- assignee: georg.brandl - d...@python nosy: +d...@python ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7678 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7678] subprocess.Popen pipeline example code in the documentation is lacking
New submission from Steven K. Wong slid...@hotmail.com: The example code at http://www.python.org/doc/2.6.2/library/subprocess.html#replacing-shell-pipeline should be updated to add the close() call noted below: output=`dmesg | grep hda` == p1 = Popen([dmesg], stdout=PIPE) p2 = Popen([grep, hda], stdin=p1.stdout, stdout=PIPE) p1.stdout.close() # - this line is not in the doc, but we should add it output = p2.communicate()[0] The parent process does not use p1.stdout after passing it to p2, so it should close p1.stdout after that. If it is not closed, there is a possibility for p1's process to never terminate if p2's process fails. The following code demonstrate this situation: from subprocess import Popen, PIPE import time # p1 is a program that writes lots of data to the pipe cmd = ['cat', 'a_large_file'] p1 = Popen(cmd, stdout=PIPE) # p2 is a program that fails without reading much data from the pipe cmd = ['python', '-c', 'import time; time.sleep(5); asdf'] p2 = Popen(cmd, stdin=p1.stdout, stdout=PIPE) output = p2.communicate()[0] while p1.poll() is None: # it loops forever print 'sleep a bit' time.sleep(1) -- assignee: georg.brandl components: Documentation messages: 97606 nosy: georg.brandl, steven.k.wong severity: normal status: open title: subprocess.Popen pipeline example code in the documentation is lacking versions: Python 2.6 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7678 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
