How do I actually set up an environment for writing C extensions?

Python Help
1

The documentation for the C API seems to skip a step; it launches directly into an explanation of coding standards, the standard headers and what they provide, etc. The “Extending Python with C or C++¶” (why is this separated?) section, similarly, appears to start and end with code examples. It doesn’t explain the necessary setup steps required before compilation is possible.

I assumed it wouldn’t be automatic simply because I have Python and gcc on my system, but just to verify:

$ gcc empty.c 
empty.c:2:10: fatal error: Python.h: No such file or directory
    2 | #include <Python.h>
      |          ^~~~~~~~~~
compilation terminated.

Where exactly are the header files supposed to be; how am I intended to obtain them (only as part of the entire repository? It’s not my intent to fork Python here yet); and how is the compiler intended to know where to look for them?

1 Like
2

You might need to separately install the Python development package for your system. On Debian, I can apt install python3 to have the Python runtime, but to build extensions, apt install python3-dev is needed, to get all of those headers.

The other possibility is that you’d need to tell GCC where to find those headers. It’s common to use pkg-config for this purpose:

rosuav@sikorsky:~/tmp$ cat empty.c
#include <Python.h>

int main() {return 0;}

rosuav@sikorsky:~/tmp$ pkg-config --cflags --libs python3
-I/usr/local/include/python3.12 -L/usr/local/lib
rosuav@sikorsky:~/tmp$ gcc empty.c
empty.c:1:10: fatal error: Python.h: No such file or directory
    1 | #include <Python.h>
      |          ^~~~~~~~~~
compilation terminated.
rosuav@sikorsky:~/tmp$ gcc empty.c `pkg-config --cflags --libs python3`
rosuav@sikorsky:~/tmp$ ./a.out
rosuav@sikorsky:~/tmp$

That might be all you need. Obviously the details will depend on your exact system, though.

3

Using the C API is hard work. There are libraries that make it easier.
You might like to use one of those libraries.
Personally I use PyCxx, but then I am the maintainer.
It is packaged for fedora and debian.

4

On Windows, the header files and static library files are in subfolders of the Python folder where python.exe lives, and they’re included by default, so it’s just a case of pointing to them when using Visual Studio.