Windows virtualenv -p python2.7 fails even when python2.7.exe exists

[asottile]

The problem stems from this function which doesn't honor the windows-specific PATHEXT.

Here's a nearly-identical implementation of that function which does handle PATHEXT expansion: https://github.com/pre-commit/pre-commit/blob/e2bae300fe2794e2ece25d4cd72127238704bb1e/pre_commit/parse_shebang.py#L21-L42

distutils.spawn.find_executable has a similar special case, but only attempts .exe: https://github.com/python/cpython/blob/9648088e6ccd6d0cc04f450f55628fd8eda3784c/Lib/distutils/spawn.py#L181-L182

[pfmoore]

virtualenv -p "2.7" finds Python 2.7 direct from the registry entries, the same way as py -2.7 works, so there should be no need for this.

[asottile]

This is necessary when using conda

[asottile]

It also makes cross platform scripts which call virtualenv -ppython2.7 just work.

Also the suggested patch reduces complexity by leveraging a stdlib function instead of a home grown solution

[pfmoore]

OK. I'm not sure how much I personally care about conda (I thought the idea was that if using conda you'd use conda to create environments, not virtualenv) but if that's a reason for needing it that's fine (it's not as if it's a massive patch).

It also makes cross platform scripts which call virtualenv -ppython2.7 just work.

It doesn't, of course, because python2.7 isn't an executable on Windows.

Also the suggested patch reduces complexity by leveraging a stdlib function instead of a home grown solution

What home-grown solution do you mean? If you mean -p "2.7" then I'm a strong -1 on removing that as I use it all the time. If you just mean adding an alternative, then fine, but that doesn't "reduce" complexity (it doesn't increase it by much, though ;-)).

[asottile]

If you read the patch it should be fairly obvious what I'm referring to :) (I'm not talking about the registry bit at all)

[pfmoore]

Oh, sorry - I did read the patch, but hadn't linked what I'd read to what you were saying - my mistake, it's been a long day :-)

So yes, functionally the only difference is then that the new code will

1. Check the current directory as well as PATH
2. Add a .exe to a file that doesn't end in .exe

I'm not sure if the different behaviour over the current directory is a big deal, and I doubt anyone is likely to use anything like a .bat file (-p mypython.bat) so agreed using a standard function seems reasonable.

[asottile]

1. is already being done anyway (as the code checks afterwards here) so I think 2. is the only real difference

And I agree, the only extension that really should be cared about in this case is .exe anyway.

[asottile]

@pfmoore is the patch mergeable then?