Request PYTHON_INCLUDE_DIR and PYTHON_LIBRARY variables (or equivalent)

[ramcdona]

CMake's FindPythonLibs.cmake searches standard install locations to find a Python installation to build against when compiling C/C++ to work with Python. This generally means it finds the default system-installed Python.

Since setup-python installs specific requested versions of Python to a non-standard location, CMake won't ever find them.

It would be great if setup-python set variables (like pythonLocation) that point at the library and header files needed to build C/C++ against a specific Python. In CMake terms, these are PYTHON_INCLUDE_DIR and PYTHON_LIBRARY, but other names could be used.

The CMake scripts FindPythonLibs, FindPythonInterp, and the new FindPython2 and FindPython3 set some other variables that might also be worth adding to the list.

Finally, it would be great if all these variables were clearly documented and their existence was obvious to a user of setup-python.

[dsame]

hello @ramcdona , i created the PR to set the hints FindPython, FindPython2 and FindPython3

I hesitate we should set PYTHON_INCLUDE_DIR and PYTHON_LIBRARY variables for deprecated FindPythonLibs module - setting these variables potentially can override the default search based on ROOT_DIR. Any thougts?

[IvanZosimov]

📟 Just a gentle ping, @ramcdona

[ramcdona]

I'm sorry, I thought I was included on this review by mistake. As a GH Actions user (not developer), I don't know how to test this change in my build system to see if it resolves my problems.

Obviously, my goal is for FindPythonXXX to 'just work' when using setup-python to set a particular version.

CMake 3.12 (the version that deprecates FindPythonLibs) is pretty new in CMake world. While the CMake community is getting better at using newer versions, it still lags. This site lists what CMake version can be expected by default with most Linux distributions.

The GH Actions Ubuntu 18.04 has CMake 3.23.2, so that isn't a problem. It looks like the oldest Windows and MacOS environments also support 3.22.2.

In my own program, I only recently updated my CMAKE_MINIMUM_REQUIRED to 3.1. I have had need to support RH 7 -- which is terribly slow to progress.

Your fix (setting CMake specific variables) should make for a pretty magical experience for CMake 3.12+ users. However, it does not help someone using simple makefiles or a hand-rolled build setup. Imagine someone setting up a compiler and wanting to know what to set the -I and -L paths to. They will have to implement their own CMake-like FindPython3- like system to convert pythonLocation into the information they need.

So, to me, having variables that contain the information implied by PYTHON_INCLUDE_DIR and PYTHON_LIBRARY is a good general purpose solution (independent of CMake). If they had generic (non-CMake aligned) names -- and those names were documented -- then a CMake user could access them and pass them in their GH Actions via -DPYTHON_INCLUDE_DIR=$pythonIncludeDir and -DPYTHON_LIBRARY=$pythonLibrary.

So, my initial request was for setup-python to set some variables that could reasonably be expected by anyone who needs to compile against the desired version of Python. If those variables were clearly documented, said user could probably figure out how to make things work for their build system.

Your solution goes above and beyond for CMake users (very cool) and is almost magical enough to not even need documentation (though the setup-python docs should be mentioned that it is expected to magically work with FindPython3).

I am certainly not the grand architect of GitHub Actions -- so I won't claim to dictate what is the right philosophical direction here.

Either way, it would be great to add some documentation (perhaps here) to inform users about these additional variables and their intended consequences. While you're at it, documenting the consequences of setup-python with "e.g." (which is perhaps an incomplete list) is fairly non-satisfying.

With this setting, the action will add/update environment variables (e.g. PATH, PKG_CONFIG_PATH, pythonLocation) for python to just work out of the box.

If that is a complete list, then OK, but it 'feels' like an incomplete list -- and the user has no way to find a complete list (including what they are expected to contain or mean). A bulleted list of all variables set by setup-python would be much appreciated.

[dsame]

@ramcdona currently we have python tool python3-config installed that does exactly that you have requested and it is well known and documented tool.

python3-config --includes produces the output
-I/Library/Frameworks/Python.framework/Versions/3.8/include/python3.8 -I/Library/Frameworks/Python.framework/Versions/3.8/include/python3.8 and can be used for gcc builds as

gcc `python3-config --includes` ...

This is a preferable way to get the python configuration and we should avoid to mimic the same functionality because of possible unpredictable interferences.

The setting the hints for cmake though was a good idea and we already implemented it, thank you.