module.py:

om subprocess import Popen, PIPE
pid = Popen(['whoami'],stdout=PIPE,stderr=PIPE)
print pid.communicate()

main.py:

import module

Running module.py directly produces the desired result.  Running main.py, however, produces the following on Python 2.5.1c1 (release25-maint, Apr 12 2007, 21:00:25), i.e., the version of Python that is included in Ubuntu Feisty Fawn:

Exception exceptions.AttributeError: "'NoneType' object has no attribute 'maxint'" in <bound method Popen.__del__ of <subprocess.Popen object at 0xb7d49f0c>> ignored

The same script works in Python 2.4.