It really annoys me that the string "3.4" is hardcoded in several places in the code, instead of being in one place that it is pulled from, but I guess there's no easy way to do that?

This PR changes the code to have that number appear only once in the code, namely in backend_bases.py. Any descendent backend can import _has_pil.

Or are you saying the documentation should pull it from the code?

Yeah, ideally. Presumably it's also defined in a pip requirements file somewhere too.

Yeah, ideally.

I'd agree, but I don't know how that would be done with Sphinx.

Presumably it's also defined in a pip requirements file somewhere too.

I don't think so because Pillow is not actually a requirement, just an optional thing, which, if present, allows to have further functionality included.

Don‘t know either how it could be done with Sphinx. But since we‘ll rarely change the version dependency, it’s ok to hard code in the docs.