How setuptools finds Visual Studio compiler

[Mark531]

Hello,

I have a question about the setuptools package: how does it find the Visual Studio compiler when it compiles a C++ extension on Windows? From the documentation (https://setuptools.pypa.io/en/latest/userguide/ext_modules.html), I understand that the compiler is looked for in the sysconfig variables CC, CXX or CSHARED, or in the environment variables CC, CPP or CXX.

Though, when I call python -m sysconfig from an Anaconda prompt, I don't see any of the interesting variables and when I call set from a VS Developer Command Prompt, I don't see any of the interesting environment variables either. So, how does it work?

Thanks in advance,
Mark

[abravalheri]

Setuptools uses vswhere to find modern versions of the toolchain.

https://github.com/pypa/setuptools/blob/main/setuptools/msvc.py

[Mark531]

Thanks for pointing the source file that handles it. I see the code is very specific to Microsoft VS... So, first it looks for vswhere.exe then executes it to find the file vcvarsall.bat to know the last version and then it executes the batch file, then it dumps the environment variables... and I'm lost. :) How complex...