$ pex setuptools==20.10.1
Python 2.7.10 (default, Dec 16 2015, 14:09:45) 
[GCC 4.2.1 Compatible Apple LLVM 7.0.2 (clang-700.1.81)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from setuptools.extern.six.moves import filterfalse, map
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/private/var/folders/3t/xkwqrkld4xxgklk2s4n41jb80000gn/T/tmphAri1w/.deps/setuptools-20.10.1-py2.py3-none-any.whl/setuptools/__init__.py", line 11, in <module>
    from setuptools.extern.six.moves import filterfalse, map
  File "/private/var/folders/3t/xkwqrkld4xxgklk2s4n41jb80000gn/T/tmphAri1w/.deps/setuptools-20.10.1-py2.py3-none-any.whl/setuptools/extern/__init__.py", line 1, in <module>
    from pkg_resources.extern import VendorImporter
ImportError: No module named extern