Errors installing packages dependent on python when pyenv installed

[ndevenish]

I've got pyenv installed and activated, through homebrew. I had activated a python3 environment, when I ran homebrew to install some things - crucially, this means that the python executable in the PATH works, but just shows an error (with non-zero return value). Firstly, when it attempts to get the python user packages in python.rb:

def self.user_site_packages(python)
    Pathname.new(`#{python} -c "import site; print(site.getusersitepackages())"`.chomp)
end

It appears to run python without checking the success of the return - which failed, which leads to messages like these (from e.g. caveats.rb:87@b33f0):

If you need Python to find bindings for this keg-only formula, run:
  echo /usr/local/opt/opencv3/lib/python2.7/site-packages >> /usr/local/lib/python2.7/site-packages/opencv3.pth
  mkdir -p 
  echo 'import site; site.addsitedir("/usr/local/lib/python2.7/site-packages")' >> homebrew.pth

e.g. spurious and incorrect commands.

Worse, I seem to have gotten several of the "python not available" messages during installation of packages, meaning I now have no idea if the package installation worked or not, because homebrew threw no errors.

I'd probably suggest checking the return value of python calls, or at least checking something works on startup - brew doctor won't even pick up this issue, but ideally installing new packages would fail also.

[MikeMcQuaid]

We don't support using pyenv. We'll accept PRs for this but we're not actively working on it at this time.