$ virtualenv test -p python2.7
Running virtualenv with interpreter /usr/bin/python2.7
New python executable in test/bin/python2.7
Also creating executable in test/bin/python
Traceback (most recent call last):
  File "/home/eliu/.dotfiles/test/lib/python2.7/site.py", line 67, in <module>
    import os
  File "/home/eliu/.dotfiles/test/lib/python2.7/os.py", line 398, in <module>
    import UserDict
  File "/home/eliu/.dotfiles/test/lib/python2.7/UserDict.py", line 83, in <module>
    import _abcoll
  File "/home/eliu/.dotfiles/test/lib/python2.7/_abcoll.py", line 11, in <module>
    from abc import ABCMeta, abstractmethod
  File "/home/eliu/.dotfiles/test/lib/python2.7/abc.py", line 8, in <module>
    from _weakrefset import WeakSet
ImportError: No module named _weakrefset
ERROR: The executable test/bin/python2.7 is not functioning
ERROR: It thinks sys.prefix is '/home/eliu/.dotfiles' (should be '/home/eliu/.dotfiles/test')
ERROR: virtualenv is not compatible with this system or executable