[issue41965] distutils.spawn.find_executable() fails to find .py files on Windows

[Alexander Todorov]

New submission from Alexander Todorov <atodorov at otb.bg>:

As part of installing python-bugzilla via pip it searches for `rst2man` or `rst2man.py`, see:
https://github.com/python-bugzilla/python-bugzilla/blob/master/setup.py#L81

on Windows venvs there is venv\Scripts\rst2man.py (no .exe or without suffix) and when you call find_executable('rst2man.py') if doesn't find it.


The trouble is in this code snippet:

```
    _, ext = os.path.splitext(executable)
    if (sys.platform == 'win32') and (ext != '.exe'):
        executable = executable + '.exe'
```

`ext` here is `.py` and the if condition executes its body so the executable to search for becomes `rst2man.py.exe` which doesn't exist.

The extension check has been like that for more than 20 years:
https://github.com/python/cpython/commit/69628b0ad10f89a65902f5b911d1040ed9ae1ca2

but IMO it should be 

```
    if (sys.platform == 'win32') and (ext == ''):
        executable = executable + '.exe'
```

i.e. add `.exe` only if the file we're looking for doesn't already have an extension.


Let me know what you think? I can submit a PR for this.


Related issues:

- https://bugs.python.org/issue2200

- https://bugs.python.org/issue39260

----------
components: Distutils
messages: 378150
nosy: Alexander.Todorov, dstufft, eric.araujo
priority: normal
severity: normal
status: open
title: distutils.spawn.find_executable() fails to find .py files on Windows
type: behavior

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41965>
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