id	summary	reporter	owner	description	type	status	priority	milestone	component	version	severity	resolution	keywords	cc
267	python: Piping via subprocess.Popen is broken	dmik		"While using `subprocess.PIPE` works per se (i.e. you may read from this pipe later on in python code), chaining several processes together doesn't.

Consider this snippet:
{{{
import os, subprocess

os.putenv ('LANG', 'en_US')

cmd1 = ['cat', 't.py']
cmd2 = ['grep', 'cmd']

proc1 = subprocess.Popen (cmd1, stdout = subprocess.PIPE)
proc2 = subprocess.Popen (cmd2, stdin = proc1.stdout)

rc = proc2.wait ()
print '*** proc2 rc', rc

rc = proc1.wait ()
print '*** proc1 rc', rc
}}}

On OS/2 (python 2.7.6-18.oc00) it gives the following output:
{{{
grep: (standard input): Operation not supported on socket
*** proc2 rc 2
*** proc1 rc 0
}}}

Expected result (tested on macOS):
{{{
cmd1 = ['cat', 't.py']
cmd2 = ['grep', 'cmd']
proc1 = subprocess.Popen (cmd1, stdout = subprocess.PIPE)
proc2 = subprocess.Popen (cmd2, stdin = proc1.stdout)
*** proc2 rc 0
*** proc1 rc 0
}}}

I.e. the child process fails to read from its stdin (which is a pipe connected to the parent's stdout) on OS/2.

Note that if you replace `cat t.py | grep cmd` with e.g. `rpm2cpio MYRPM | cpio -idm`, the error will be as follows:
{{{
2 blocks
cpio: error closing archive: Bad file number
}}}
meaning that cpio worked per se (files unpacked correctly) but failed to close the input stream.

Also note that both examples work smoothly as shell commands from under dash or ash.

It looks like we're using pipes (or socket pairs?) incorrectly in Python."	defect	closed	major		python		medium	fixed