virtualenv on macOS uses nonexistent python interpreter

Question

When I run virtualenv , I get this:

$ virtualenv
-bash: /usr/local/bin/virtualenv: /usr/local/opt/python/bin/python2.7: bad interpreter: No such file or directory

virtualenv only started behaving this way today. It worked yesterday. It breaks because virtualenv is a Python script using a nonexistent Python interpreter:

$ head -1 $(which virtualenv)
#!/usr/local/opt/python/bin/python2.7

On my machine, /usr/local/opt/python is a symlink to a Python 3.6 directory:

$ ls -l /usr/local/opt/python
lrwxr-xr-x  1 jim  admin  24  2 Mar 13:45 /usr/local/opt/python -> ../Cellar/python/3.6.4_3

As expected, the Python 3.6 directory does not contain a bin/python2.7 :

$ ls /usr/local/Cellar/python/3.6.4_3/bin/
2to3            idle            pip3            pydoc3.6        python3-config      python3.6m-config   wheel3
2to3-3.6        idle3           pip3.6          python          python3.6       pyvenv
easy_install        idle3.6         pydoc           python-config       python3.6-config    pyvenv-3.6
easy_install-3.6    pip         pydoc3          python3         python3.6m      wheel

virtualenv clearly expects /usr/local/opt/python to contain Python 2 material, but it only contains Python 3 material.

My /usr/local/opt/python is managed by Homebrew. I don't know the provenance of my virtualenv . How do I find out where my /usr/local/bin/virtualenv came from?

Which is to blame? My virtualenv or Homebrew?

Answer 1

The blame for this lies with pip , not Homebrew. My /usr/local/bin/virtualenv came from pip install virtualenv , which embeds an absolute link to the Python interpreter at installation time! I have opened an issue about this unidiomatic behavior .

Answer 2

Firstly, sorry for adding a separate comment here -- I lack the reputation to add a comment to @jameshfisher's answer.

I used homebrew to update python2 on macos to the latest version:

~ ❯❯❯ python2 --version
Python 2.7.15

Which creates/updates the python2 symlink in /usr/local/bin to link to that particular brew installed update:

~ ❯❯❯ ls -ahl =python2
lrwxr-xr-x  1 michael  admin    39B  3 Jul 17:11 /usr/local/bin/python2 -> ../Cellar/python@2/2.7.15_1/bin/python2

The shebang in my /usr/local/bin/virtualenv was:

~ ❯❯❯ head -1 $(which virtualenv)
#!/usr/local/opt/python/bin/python2.7

Which did not exist:

~ ❯❯❯ ls -l /usr/local/opt/python/bin/python2.7
ls: /usr/local/opt/python/bin/python2.7: No such file or directory

So modifying the shebang to #!/usr/local/bin/python2 to use the brew installed updated python2 version was the most appropriate way to go:

~ ❯❯❯ virtualenv --version
15.1.0

✨🐟✨

A bit of a red herring for me was that I had mistakenly assumed typing which python would give me the path to my version of python2 :

~ ❯❯❯ which python
/Users/michael/.pyenv/shims/python
~ ❯❯❯ which python2
/usr/local/bin/python2
~ ❯❯❯ which python3
/Users/michael/.pyenv/shims/python3

~ ❯❯❯ /Users/michael/.pyenv/shims/python --version
Python 3.7.0

I had forgotten that I had set pyenv global to python 3.7.0 . Please don't fall into that trap as I did! ✨😄✨

Answer 3

Same problem on my Mac. Maybe it got broken when I updated to Mojave? Who knows.

Resolved with a brew install of Python 2:

brew install python2

This now takes over from my factory-installed Python 2.7 and gives me a new virtualenv that works:

$ which virtualenv
/usr/local/bin/virtualenv