Windows registry Python discovery (PEP 514) not working for "cpython" specs for distributions by unknown orgs

[faph]

Issue

On Windows:

$ python --version
Python 3.11.1
$ python -m virtualenv --version
virtualenv 20.17.1 from C:\<some path>\tools\python3.11\latest\Lib\site-packages\virtualenv\__init__.py
$ python -m virtualenv .venv -p cpython3.10 -vv

Output:

180 setup logging to DEBUG [DEBUG report:35]
195 find interpreter for spec PythonSpec(implementation=cpython, major=3, minor=10) [INFO builtin:56]
195 proposed PythonInfo(spec=CPython3.11.1.final.0-64, exe=C:\<some path>\tools\python3.11\latest\python.exe, platform=win32, version='3.11.1 (tags/v3.11.1:a7a450f, Dec
6 2022, 19:58:39) [MSC v.1934 64 bit (AMD64)]', encoding_fs_io=utf-8-utf-8) [INFO builtin:63]
202 discover PATH[0]=C:\<some path>\tools\zip\latest\bin\ [DEBUG builtin:108]
205 filesystem is not case-sensitive [DEBUG info:24]
206 discover PATH[1]=C:\<some path>\tools\yq\latest [DEBUG builtin:108]
...
249 RuntimeError: failed to find interpreter for Builtin discover of python_spec='cpython3.10' [ERROR __main__:61]

Seems this is due to logic here: https://github.com/pypa/virtualenv/blob/main/src/virtualenv/discovery/windows/__init__.py#L23

It lists PythonCore and ContinuumAnalytics as the 2 organizations mapping to the CPython implementation. That logic is unfortunate, since many more organizations can decide to distribute CPython. For example, my firm uses a different organization name in the Windows registry, compliant with PEP 514 https://peps.python.org/pep-0514/.

I guess the solution should be similar to how the implementation is looked up for PATH OS environment variable entries: execute the Python binary and inspect the "pyinfo" output.

[faph]

For the avoidance of doubt, none of my Python interpreters are available on PATH.

If I do add the relevant interpreters to PATH, then the discover works as expected.

Also, if I change the Windows Registry keys, and use the PythonCore organization name, it also works.

[faph]

See also #1796 which introduced the organization name to implementation mapping.

[faph]

An alternative solution could be to accept additional custom keys. PEP 514 gives the following example:

HKEY_CURRENT_USER\Software\Python\PythonCore\3.6
    (Default) = (value not set)
    DisplayName = "Python 3.6 (64-bit)"
    SupportUrl = "http://www.python.org/"
    Version = "3.6.0"
    SysVersion = "3.6"
    SysArchitecture = "64bit"

Which could be extended for example using SysImplementation = "CPython".

Downside is that such a key would be by convention and it may be undesirable to expect Python distributors to set such a key.

The advantage would be speed since it would no longer require the interpreter to be executed.

[gaborbernat]

PR welcome.

[faph]

Sure. As an initial improvement, would the “SysImplementation“ solution be ok, @gaborbernat ?

[gaborbernat]

Sure. But note this must not be a breaking change, and what's there should still work as is today.

[faph]

@gaborbernat I have started to experiment with a solution to remove the Windows Registry-based pre-filtering. Let me know if that's a direction you're willing to consider.

[faph]

Thank you for your help on this @gaborbernat

[gaborbernat]

Thanks for the PR.

[MeCorey]

Sure. As an initial improvement, would the “SysImplementation“ solution be ok, @gaborbernat ?

hmm...possibility