[New-bugs-announce] [issue22442] subprocess.check_call hangs on large PIPEd data.

juj report at bugs.python.org
Fri Sep 19 15:56:39 CEST 2014

New submission from juj:

On Windows, write


import subprocess

def ccall(cmdline, stdout, stderr):
  proc = subprocess.Popen(['python', 'b.py'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
  if proc.returncode != 0: raise subprocess.CalledProcessError(proc.returncode, cmdline)
  return 0

# To fix subprocess.check_call, uncomment the following, which is functionally equivalent:
# subprocess.check_call = ccall

subprocess.check_call(['python', 'b.py'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
print 'Finished!'

Then write b.py:

import sys

str = 'aaa'
for i in range(0,16): str = str + str
for i in range(0,2): print >> sys.stderr, str
for i in range(0,2): print str

Finally, run 'python a.py'. The application will hang. Uncomment the specicied line to fix the execution.

This is a documented failure on the python subprocess page, but why not just fix it up directly in python itself?

One can think that modifying stdout or stderr is not the intent for subprocess.check_call, but python certainly should not hang because of that.

components: Library (Lib)
messages: 227095
nosy: juj
priority: normal
severity: normal
status: open
title: subprocess.check_call hangs on large PIPEd data.
versions: Python 2.7

Python tracker <report at bugs.python.org>

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