Arch Linux

Description: pip exits with an exception whenever I try to install a python package.

Exception:
Traceback (most recent call last):
File "/usr/lib/python3.4/site-packages/pip/basecommand.py", line 232, in main
status = self.run(options, args)
File "/usr/lib/python3.4/site-packages/pip/commands/install.py", line 339, in run
requirement_set.prepare_files(finder)
File "/usr/lib/python3.4/site-packages/pip/req/req_set.py", line 229, in prepare_files
req_to_install.check_if_exists()
File "/usr/lib/python3.4/site-packages/pip/req/req_install.py", line 928, in check_if_exists
self.satisfied_by = pkg_resources.get_distribution(self.req)
File "/usr/lib/python3.4/site-packages/pip/_vendor/pkg_resources/__init__.py", line 461, in get_distribution
dist = get_provider(dist)
File "/usr/lib/python3.4/site-packages/pip/_vendor/pkg_resources/__init__.py", line 341, in get_provider
return working_set.find(moduleOrReq) or require(str(moduleOrReq))[0]
File "/usr/lib/python3.4/site-packages/pip/_vendor/pkg_resources/__init__.py", line 870, in require
needed = self.resolve(parse_requirements(requirements))
File "/usr/lib/python3.4/site-packages/pip/_vendor/pkg_resources/__init__.py", line 740, in resolve
env = Environment(self.entries)
File "/usr/lib/python3.4/site-packages/pip/_vendor/pkg_resources/__init__.py", line 927, in __init__
self.scan(search_path)
File "/usr/lib/python3.4/site-packages/pip/_vendor/pkg_resources/__init__.py", line 957, in scan
self.add(dist)
File "/usr/lib/python3.4/site-packages/pip/_vendor/pkg_resources/__init__.py", line 977, in add
dists.sort(key=operator.attrgetter('hashcmp'), reverse=True)
TypeError: unorderable types: NoneType() < str()


Additional info:
* this is a fresh install of python-pip
* pip 6.0.6 from /usr/lib/python3.4/site-packages (python 3.4)


Steps to reproduce:
# sudo pacman -S --needed python-pip
# sudo pip install ptpython