I'm seeing differing behaviour with subprocess.Popen(..., close_fds = False) between 3.2 and 3.4. The docs don't say this is meant to be the case as far as I can see.

Python 3.2.3 on Debian Wheezy
=============================

>>> import subprocess
>>> import os
>>> r,w = os.pipe()
>>> p = subprocess.Popen('ls /dev/fd/*', shell = True, close_fds = False)
>>> ls: cannot access /dev/fd/5: No such file or directory
/dev/fd/0  /dev/fd/1  /dev/fd/2  /dev/fd/3  /dev/fd/4

Python 3.4.2 on Arch Linux
==========================

>>> import subprocess
>>> import os
>>> r,w = os.pipe()
>>> p = subprocess.Popen('ls /dev/fd/*', shell = True, close_fds = False)                                                                                                            
>>> ls: cannot access /dev/fd/3: No such file or directory
/dev/fd/0  /dev/fd/1  /dev/fd/2

In 3.4 even though close_fds is False the fds are closed in the child. Using pass_fds works around this though I would like to know if this is a bug, documentation issue, or am I missing something here?

File descriptors are not closed, but not inherited neither, in Python 3.4. See the PEP 446.

To have a reliable behaviour on all platforms and all Python versions, just use the pass_fds parameter.

https://docs.python.org/dev/library/os.html#os.pipe

Changed in version 3.4: The new file descriptors are now non-inheritable.

If you don't use the subprocess module, you may use os.set_inheritable().
https://docs.python.org/dev/library/os.html#os.set_inheritable

Ah, got it. Didn't see the note on the os.pipe() docs. Thanks. Closing. Sorry for the noise.