Using stderr=subprocess.STDOUT causes Python 3.0 (RC1 from Ubuntu 8.10)
to raise AttributeError, important code snippet (whole test program
attached):

proc = subprocess.Popen(['whoami'], stdout=subprocess.PIPE,
stderr=subprocess.STDOUT)
stdout, stderr = proc.communicate()


nelchael@nelchael-vbox ~$ python2.5 --version
Python 2.5.2
nelchael@nelchael-vbox ~$ python2.5 test-subprocess.py
('stdout:', 'nelchael\n')
('stderr:', None)
nelchael@nelchael-vbox ~$ python3 --version
Python 3.0rc1+
nelchael@nelchael-vbox ~$ python3 test-subprocess.py
Traceback (most recent call last):
  File "test-subprocess.py", line 4, in <module>
    stdout, stderr = proc.communicate()
  File "/usr/lib/python3.0/subprocess.py", line 663, in communicate
    stdout = self._fo_read_no_intr(self.stdout)
AttributeError: 'Popen' object has no attribute '_fo_read_no_intr'
nelchael@nelchael-vbox ~$

This "_fo_read_no_intr" method does not exist anywhere in the standard 
python code.

A quick Google search reveals that it certainly comes from a patch 
proposed by the Ubuntu maintainers:
http://patches.ubuntu.com/p/python2.5/extracted/subprocess-eintr-
safety.dpatch

It is very likely that this patch (for 2.5) did not apply correctly to 
the 3.0 source code.
In any case, this is not a Python problem.