cannot build: Could not find a version that satisfies the requirement sphinxcontrib-ansi

[timotheecour]

pip install --user -r requirements.txt --upgrade
Could not find a version that satisfies the requirement sphinxcontrib-ansi (from -r requirements.txt (line 5)) (from versions: )
No matching distribution found for sphinxcontrib-ansi (from -r requirements.txt (line 5))

pip search sphinxcontrib returns lots of things but
pip search sphinxcontrib-ansi | grep sphinxcontrib-ansi is empty