'pip3 --version' failing with a SyntaxErro

Question

This all began when I set out to install the Requests library for Python 3 (I'm running on OSX Mavericks with Python 2.7.5 (installed by brew install python) and 3.4.2 (installed by brew install python3). When I run pip3 --version (or anything related to the pip3 command) I see this:

$ pip3 --version
Traceback (most recent call last):
  File "/usr/local/bin/pip3", line 7, in <module>
    from pip import main
  File "/usr/local/lib/python3.4/site-packages/pip/__init__.py", line 11, in <module>
    from pip.vcs import git, mercurial, subversion, bazaar  # noqa
  File "/usr/local/lib/python3.4/site-packages/pip/vcs/mercurial.py", line 9, in <module>
    from pip.download import path_to_url
  File "/usr/local/lib/python3.4/site-packages/pip/download.py", line 22, in <module>
    from pip._vendor import requests, six
  File "/usr/local/lib/python3.4/site-packages/pip/_vendor/requests/__init__.py", line 53, in <module>
    from .packages.urllib3.contrib import pyopenssl
  File "/usr/local/lib/python3.4/site-packages/pip/_vendor/requests/packages/urllib3/contrib/pyopenssl.py", line 49, in <module>
    from ndg.httpsclient.ssl_peer_verification import SUBJ_ALT_NAME_SUPPORT
  File "/usr/local/Cellar/python3/3.4.2_1/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/ndg/httpsclient/ssl_peer_verification.py", line 17
    except ImportError, e:
                      ^
SyntaxError: invalid syntax

When I run the Python 2.7.5 version I see this:

$ pip --version
pip 1.5.6 from /Library/Python/2.7/site-packages/pip-1.5.6-py2.7.egg (python 2.7)

Just for sanity purposes Here is what when I see when I enter the interactive interpreters:

$ python3
Python 3.4.2 (default, Oct 19 2014, 17:52:17) 
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.51)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> exit()

$ python
Python 2.7.5 (default, Mar  9 2014, 22:15:05) 
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.0.68)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> exit()

A lot of the other answers related to updating pip3 suggest that I update pip3 with this commend pip3 install --upgrade pip which gives the same error, or I use easy_install -U pip but because of how brew sets up the Pythons, it only updates the Python 2.7.5 version (there is no easy_install3). Any ideas?

Answer 1

The root problem is that you somehow got a Python 2.x-only package installed into your 3.x site-packages.

Underlying that, you've actually got two different Python 2.7 installations (Apple's and Homebrew's) crossed with each other, which may have something to do with how you got a 2.7 package into 3.x as well…

Anyway, the reason this is breaking pip is that pip has various optional dependencies that it tries to import if present, and some of them do the same, and so on, and ultimately, starting up pip is importing the ndg-httpsclient package.

I'm not sure how you got that package. A standard Homebrew 3.x looks in two extra site-packages directories (fire up python3 then import sys; print(sys.path) to see all of the places it looks, both stdlib and site) beyond the one that pip3 installs into.

In this case, you've somehow installed the 2.x version of ndg-httpsclient into /usr/local/Cellar/python3/3.4.2_1/Frameworks/Python.framework/Versions/3.4/lib/‌​python3.4/site-packages.

Since you didn't install it with pip—and, more to the point, since you can't run pip in the first place—you can't just pip uninstall it. So:

rm -rf /usr/local/Cellar/python3/3.4.2_1/Frameworks/Python.framework/Versions/3.4/lib/‌​python3.4/site-packages/ndg*

This could break some other packages that depend on it. Once you get things working, you can use pip3 list to see all the site packages you've installed and test them out. If you want to be paranoid, do something like this:

$ pip3 list > mypackages
$ rm -rf <each site-package directory>
$ brew uninstall python3
$ brew install python3
$ pip3 install -r mypackages

You might want to similarly clean up your Homebrew 2.7 (or just scrap it and only use Apple's—especially since I'm pretty sure you're running Apple's anyway), and the site-packages for the Apple 2.7 (but not Apple's Python itself, of course, because you can't uninstall that).