uv not detecting system installed Python installations of other architecture on Windows

[schlamar]

Summary

Expected:

> py -0p
 -V:3.11 *        C:\Program Files\Python311\python.exe
 -V:3.11-32       C:\Program Files (x86)\Python311-32\python.exe
 -V:3.10          C:\Program Files\Python310\python.exe
 -V:3.10-32       C:\Program Files (x86)\Python310-32\python.exe
 -V:3.9-32        C:\Users\<user>\AppData\Local\Programs\Python\Python39-32\python.exe

Actual (3.11-32 and 3.10-32 is missing):

> .\uv python list --only-installed --verbose
←[34mDEBUG←[39m uv 0.5.27 (73e9928d4 2025-02-03)
←[34mDEBUG←[39m Searching for any Python interpreter in managed installations, search path, or registry
←[34mDEBUG←[39m Searching for managed installations at `C:\Users\<user>\AppData\Roaming\uv\python`
←[34mDEBUG←[39m Found `cpython-3.11.9-windows-x86_64-none` at `C:\Program Files\Python311\python.exe` (search path)
←[34mDEBUG←[39m Found `cpython-3.11.9-windows-x86_64-none` at `C:\Program Files\Python311\python.exe` (registry)
←[34mDEBUG←[39m Found `cpython-3.10.11-windows-x86_64-none` at `C:\Program Files\Python310\python.exe` (registry)
←[34mDEBUG←[39m Found `cpython-3.9.13-windows-x86-none` at `C:\Users\<user>\AppData\Local\Programs\Python\Python39-32\python.exe` (registry)
cpython-3.11.9-windows-x86_64-none     C:\Program Files\Python311\python.exe
cpython-3.10.11-windows-x86_64-none    C:\Program Files\Python310\python.exe
cpython-3.9.13-windows-x86-none        C:\Users\<user>\AppData\Local\Programs\Python\Python39-32\python.exe

Platform

Windows Server 2022

Version

uv 0.5.27 (73e9928 2025-02-03)

Python version

Python 3.11.9

[zanieb]

I presume py finds these from the registry? cc @konstin

[konstin]

32-bit pythons show for me locally, can you share the output of Get-ChildItem -Path "HKCU:\Software\Python" -Recurse -Depth 2 and Get-ChildItem -Path "HKLM:\Software\Python" -Recurse -Depth 2?

[schlamar]

The issue is probably how Microsoft maps 32bit and 64bit data in the registry. To read 32bit processes from 64bit process and vice versa you have to use specific flags - see https://learn.microsoft.com/en-us/windows/win32/winprog64/accessing-an-alternate-registry-view

So reading "HKLM:\Software\Python" with Powershell depends on which Powershell version you use. Normal (x64) returns the two 64bit Python installations. Reading with Powershell x86 returns the two Python 32bit installations.

[schlamar]

Running 64bit uv I get 64bit system installed Python versions only and running 32bit uv I get 32bit system installed versions only. So uv ignores how Microsoft maps 32bit / 64bit process data to HKLM and only reads data for the current architecture.

User installed Python versions work (because HKCU is not affected by the 32bit / 64bit registry mapping).

[schlamar]

This affects probably all use cases regarding Python discovery, no only python list. For example uv venv -p cpython-3.11-windows-x86-none --no-python-downloads fails with "No interpreter found" running a 64bit uv although it is globally installed.

[eabase]

Huh, this is weird, from Admin pwsh, I get permission issue:

# Get-ChildItem -Path "HKLM:\Software\Python" -Recurse -Depth 2

Get-ChildItem: Requested registry access is not allowed.
Get-ChildItem: Requested registry access is not allowed.
Get-ChildItem: Requested registry access is not allowed.

    Hive: HKEY_LOCAL_MACHINE\Software\WOW6432Node