The addition of the _posixsubprocess module in 3.2 introduced a change of behaviour when passing an empty dict (or other false value besides None) as env:

python3.1 -c 'import subprocess; print(subprocess.Popen(["env"], env={}, stdout=subprocess.PIPE).communicate())'
(b'', None)

python3.2 -c 'import subprocess; print(subprocess.Popen(["env"], env={}, stdout=subprocess.PIPE).communicate())'
(b'LC_MONETARY=C\nSHELL=/bin/bash\nTERM=scr....', None)

The test for 'env' being the default (None) is not explicit enough.

New changeset b5963fceddad by Victor Stinner in branch '3.2':
Close #12383: Fix subprocess module with env={}: don't copy the environment
http://hg.python.org/cpython/rev/b5963fceddad

New changeset 10ecf8576eb2 by Victor Stinner in branch 'default':
(merge 3.2) Close #12383: Fix subprocess module with env={}: don't copy the
http://hg.python.org/cpython/rev/10ecf8576eb2

> The addition of the _posixsubprocess module in 3.2 introduced
> a change of behaviour when passing an empty dict
> (or other false value besides None) as env: ...

This bug was introduced by the commit (768722b2ae0a) introducing _posixsubprocess.

Thanks for the fix, I added an unit test.

The test appears to be failing on the buildbots:

http://www.python.org/dev/buildbot/all/builders/x86%20Ubuntu%20Shared%203.2/builds/370

That failure is likely due to the environment being empty causing the subprocess to be unable to run.  Notice this error message further up:

test_empty_env (test.test_subprocess.ContextManagerTests) ... /srv/buildbot/buildarea/3.2.bolen-ubuntu/build/python: error while loading shared libraries: libpython3.2dm.so.1.0: cannot open shared object file: No such file or directory
FAIL

Looking at the environment at the top of the buildbot run log I'm not sure what it would be.

On Mac OS X, the failure is different:

======================================================================
FAIL: test_empty_env (test.test_subprocess.ProcessTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.x.parc-tiger-1/build/Lib/test/test_subprocess.py", line 400, in test_empty_env
    self.assertEqual(stdout.strip(), b"0")
AssertionError: b'1' != b'0'

http://www.python.org/dev/buildbot/all/builders/PPC%20Tiger%203.x/builds/2059/steps/test/logs/stdio

Maybe test_empty_env() should pass LD_LIBRARY_PATH to child process.

New changeset 8d46e84cd812 by Victor Stinner in branch '3.2':
Issue #12383: skip test_empty_env() if compiled is compiled in shared mode
http://hg.python.org/cpython/rev/8d46e84cd812

New changeset d1d5a7392e39 by Victor Stinner in branch 'default':
(merge 3.2) Issue #12383: skip test_empty_env() if compiled is compiled in
http://hg.python.org/cpython/rev/d1d5a7392e39

> Maybe test_empty_env() should pass LD_LIBRARY_PATH to child process.

The idea of the test is to test an empty environment: if we pass one variable, it is no more an empty environment.

I changed the test to skip it if Python is compiled in shared mode.

New changeset da3af4b131d7 by Victor Stinner in branch '3.2':
Issue #12383: fix test_empty_env() of subprocess on Mac OS X
http://hg.python.org/cpython/rev/da3af4b131d7

New changeset 29819072855a by Victor Stinner in branch 'default':
(merge 3.2) Issue #12383: fix test_empty_env() of subprocess on Mac OS X
http://hg.python.org/cpython/rev/29819072855a

New changeset 52c5f80122dd by Victor Stinner in branch '3.2':
Issue #12383: skip test_empty_env() of subprocess on Windows
http://hg.python.org/cpython/rev/52c5f80122dd

New changeset 93cd98782f47 by Victor Stinner in branch 'default':
(merge 3.2) Issue #12383: skip test_empty_env() of subprocess on Windows
http://hg.python.org/cpython/rev/93cd98782f47

All Python 3.x buildbots are green again (except FreeBSD 7.2, but the failures are not related to this issue).