distutils Extension arguments -- include vs depends vs source?

Question

I'm trying to understand the dependency structure of pandas' cython extensions in setup.py.

distutils.extension.Extension has arguments sources, depends, and include_dirs, and I can't figure out the difference between these. In particular, there are a bunch of places in the pandas case where I can delete entries in depends (or pxdfiles) without breaking the build.

What is the distinction between these three arguments?

Update following answer from @phd: I appreciate the thought, will try to better communicate the source of my confusion.

In the pandas setup.py file linked above, the pandas._libs.tslib extension is passed to distutils.extension.Extension with the args/kwargs:

ext = Extension('pandas._libs.tslib',
    sources=['pandas/_libs/tslib.pyx',
             'pandas/_libs/src/util.pxd',
             'pandas/_libs/src/datetime/np_datetime.c',
             'pandas/_libs/src/datetime/np_datetime_strings.c',
             'pandas/_libs/src/period_helper.c'],
    depends=['pandas/_libs/src/datetime/np_datetime.h',
             'pandas/_libs/src/datetime/np_datetime_strings.h',
             'pandas/_libs/src/period_helper.h',
             'pandas/_libs/src/datetime.pxd'],
    include_dirs=['pandas/_libs/src/klib', 'pandas/_libs/src'])

Take e.g. util.pxd in the sources entry. Is this not redundant with the presence of pandas/_libs/src in the include_dirs entry? tslib imports directly from datetime.pxd which has "imports" of the form cdef extern from "datetime/np_datetime.h" and cdef extern from "datetime/np_datetime_strings.h". Are those "allowed" because of the presence of the "*.c" files in the sources or the "*.h" files in the depends or both or...

I've tried a whole bunch of permutations of removing subsets of these dependencies, have not seen many patterns in terms of which break the build.

Answer 1

See the detailed docs and the source code for build_ext command.

sources is a list of source files (*.c) to compile the extension.

depends — a list of additional files the extensions is required to compile.

include_dirs — a list of directories where a compiler will look for include (header) files (*.h).

pxdfiles are Cython-specific.