@Mariatta Do you think that this should be pinned or float upward?

I pinned it because that's how it was in .travis.yml.

https://github.com/python/cpython/blob/master/.travis.yml#L58

Actually, do you think it might be better to make .travis.yml to read from Doc/requirements.txt instead of specifying its own versions?

Let's do this. Keep it pinned for now but add a comment: # Pin sphinx to version specified in .travis.yml on the line above Sphinx in requirements.txt

Done. I think it might be better to just include python -m pip install -r Docs/requirements.txt in .travis.yml though, so that we don't have to keep two files in sync, unless there's a reason not to do so?

@epicfaace For now, the least disruptive change was to make the modification here. Ideally, there wouldn't be duplication. Would you like to open an issue suggesting the above.

Could this be specified in netlify.toml too instead of a special-purpose file?

Nope. https://www.netlify.com/docs/build-settings