I’m still looking at this, but the constraints file doesn’t seem to be taking effect for the build.
For example, if I run the following with verbose turned on.
echo "statsmodels==0.13.2" >> constraints.txt
echo "Cython==0.29.27" >> constraints.txt
pip install -v statsmodels==0.13.2 -c constraints.txt
It looks like cython 3.0.0 is somehow making it in there.
Successfully installed cython-3.0.0 numpy-1.14.5 oldest-supported-numpy-2022.11.19 scipy-1.7.3 setuptools-68.0.0 wheel-0.40.0
Same thing happens if I’m less strict about the version and specify cython less than 3.
echo "statsmodels==0.13.2" >> constraints.txt
echo "Cython<3" >> constraints.txt
pip install -v statsmodels==0.13.2 -c constraints.txt