Python prefix is incorrect

[marcaurele]

Hi,

When I do a pipsi install, the python prefix in the scripts first line is incorrect and point to the system python. I'm trying to figure why, but I can't find an explanation. Do you have any pointer where I should look? I'm using ZSH on OSX if that matters somehow.

This is the output with virtualenv -v and pip -v -v -v https://gist.github.com/marcaurele/ef8dd46b802bd0cde77a

If I do it manually, of course it works (virtualenv & pip), but that's not the point.

[RonnyPfannschmidt]

at first glance this looks like a issue on osx, i cant verify it since i don't have fit hardware

[marcaurele]

I'm eager to find the solution, let me know what i should try out.

[RonnyPfannschmidt]

right now i have no idea myself, it seels to be related to virtualenv, but im just vaugely guessing

[cjrh]

The reasons behind this problem are quite obscure, as you'll see from the fix. The necessary ingredients are Python 3, virtualenv (not venv), OS X and Homebrew. To fix the problem, you have to pop an environment variable called PYVENV_LAUNCHER before launching the subprocess. I made the following changes in pipsi.py, around line 230:

        # Install virtualenv, use the pipsi used python version by default
        args = ['virtualenv', '-p', python or sys.executable, venv_path]

        try:
            env = dict(os.environ)                                 # <<== NEW
            env.pop('__PYVENV_LAUNCHER__', None)                   # <<== NEW
            if Popen(args, env=env).wait() != 0:                   # <<== env kwarg
                click.echo('Failed to create virtualenv.  Aborting.')
                return _cleanup()

            args = [os.path.join(venv_path, BIN_DIR, 'pip'), 'install']
            if editable:
                args.append('--editable')

            if Popen(args + install_args, env=env).wait() != 0:    # <<== env kwarg
                click.echo('Failed to pip install.  Aborting.')
                return _cleanup()
        except Exception:
            _cleanup()
            raise

The following links provide more background:

pypa/virtualenv#532
pypa/virtualenv#541
pypa/virtualenv#845

Finally, I found the initial problem with (OSX+Homebrew) Python 3.6 (most of the other links refer to 3.3 -> 3.5), and the resolution above also resolves the problem on 3.6.

EDIT: finally found a more complete description of the root cause: https://bugs.python.org/issue22490#msg227579

[RonnyPfannschmidt]

@cjrh can you submit a pr? personally i am handing pipsi in a minimal workload on me mode, and a pr is far simpler to manage than needing to recreate a patch based on instructions (even if in this case it does look reasonably trivial

i also do wonder if there is any way to create a automated test for that case

[cjrh]

@RonnyPfannschmidt The problem goes away if #71 is merged, and I think that's the better solution than the hacky env var change above.