> Python 3.8 and Python 3.7 doesn't have Sphinx pinned to 2.2.0 while master does.

In 3.8, .azure-pipelines/docs-steps.yml contains:

- script: python -m pip install sphinx==1.8.2 blurb python-docs-theme

and .travis.yml contains:

- python -m pip install sphinx==1.8.2 blurb python-docs-theme

For example, the Sphinx version was changed from 1.8.1 to 1.8.2 in the CI configuration by:

commit 7f4ba4afd47f21f61de9035544809fc67d136f35
Author: Julien Palard <julien@palard.fr>
Date:   Sat Nov 24 11:35:21 2018 +0100

    Doc: Bump sphinx. (GH-10676)

--

I guess that you're talking about Doc/Makefile which uses "Sphinx" in 3.8 but "Sphinx==2.2.0" in master. Code in 3.8:

venv:
	$(PYTHON) -m venv $(VENVDIR)
	$(VENVDIR)/bin/python3 -m pip install -U pip setuptools
	$(VENVDIR)/bin/python3 -m pip install -U Sphinx blurb python-docs-theme
	@echo "The venv has been created in the $(VENVDIR) directory"