macos - Pip suddenly using wrong version of Python

Question

Having a weird problem with pip on os x.

As far as I can recall (and a quick look at my .bash_history seems to confirm) I have not made any recent changes to my configuration. Alas, the pip command seems to be suddenly using a different version of python than it was previously. Up until now I was using the command pip to manage my python2 libraries and pip3 to manage by python3 libraries. Suddenly, any attempts at running pip install fails with errors like missing parenthesis around print statements.

Here is the result of a few commands I attempted to figure out the problem:

which pip > /usr/local/bin/pip

which pip3 > /usr/local/bin/pip3

which python > /usr/local/bin/python

python version > Python 2.7.11

pip --version > pip 8.1.1 from /usr/local/lib/python3.5/site-packages (python 3.5)

So for some reason the pip command seems to be running from the PyPi2 database but in python3 now? Any ideas how to fix this?

Answer 1

I run with multiple Python versions and thus multiple pip versions as well.

Everytime, however, you update pip, you'll replace the standard pip command with the version you updated. So even pip3 install --upgrade pip will put a /usr/local/bin/pip in your system, messing up the Python 2 version.

Instead, I run pip as an (executable) module:

python3 -m pip search <package>

or

python2 -m pip search <package>

or even

python3.5 -m pip search <package>

This guarantees that your pip version always matches the Python version you want to use it for. It's somewhat longer to type, but I prefer the expliciteness of it (which, I guess, follows the Zen of Python).

Note that updating pip:

python3.5 -m pip install --upgrade pip

will still install a Python 3.5 version in /usr/local/bin/pip, but I'm simply ignoring that. Just beware of (shell) scripts that execute pip directly.