say you're installing the development build of mcomix
python3 -m pip install --user git+https://git.code.sf.net/p/mcomix/git
(you're doing it as your own user because you don't want sweeping system changes for something like an unstable build of a comic book viewer)
but it won't compile due to weird and inscrutable errors
the Ubuntu packages you must first install are: libgirepository1.0-dev
libcairo2-dev
(yes, the development headers)