$ pip install -r requirements.txt -t lib

Could not import setuptools which is required to install from a source distribution.
Traceback (most recent call last):
File "/usr/local/lib/python2.7/site-packages/pip/req/req_install.py", line 387, in setup_py
import setuptools # noqa
File "/usr/local/lib/python2.7/site-packages/setuptools/init.py", line 10, in
from setuptools.extern.six.moves import filter, filterfalse, map
File "/usr/local/lib/python2.7/site-packages/setuptools/extern/init.py", line 1, in
from pkg_resources.extern import VendorImporter
ImportError: No module named extern