python-igraph fails to build with Python 3.13.0a1.

src/_igraph/convert.c:104:11: error: implicit declaration of function tolower [-Werror=implicit-function-declaration]
  104 |     *s2 = tolower(*s2);
      |           ^~~~~~~
src/_igraph/convert.c:36:1: note: include ‘<ctype.h>’ or provide a declaration of ‘tolower’

According to https://docs.python.org/3.13/whatsnew/3.13.html:

Python.h no longer includes the <ctype.h> standard header file.
If needed, it should now be included explicitly.
For example, it provides isalpha() and tolower() functions which are locale dependent.
Python provides locale independent functions, like Py_ISALPHA() and Py_TOLOWER().
(Contributed by Victor Stinner in gh-108765.)


https://docs.python.org/3.13/whatsnew/3.13.html

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.13/fedora-rawhide-x86_64/06546789-python-igraph/

For all our attempts to build python-igraph with Python 3.13, see:
https://copr.fedorainfracloud.org/coprs/g/python/python3.13/package/python-igraph/

Testing and mass rebuild of packages is happening in copr.
You can follow these instructions to test locally in mock if your package builds with Python 3.13:
https://copr.fedorainfracloud.org/coprs/g/python/python3.13/

Let us know here if you have any questions.

Python 3.13 is planned to be included in Fedora 41.
To make that update smoother, we're building Fedora packages with all pre-releases of Python 3.13.
A build failure prevents us from testing all dependent packages (transitive [Build]Requires),
so if this package is required a lot, it's important for us to get it fixed soon.

We'd appreciate help from the people who know this package best,
but if you don't want to work on this now, let us know so we can try to work around it on our side.