coverage runs very slowly on windows with python 3.8, but not 3.7

Question

I have a flask based app, when I run coverage on the pytests in windows using python 3.8 it runs very slowly. It performs much better in python 3.7. The following are the test completion times using a the same laptop, the Ubuntu times are the same machine running as a VM.

python 3.8.2 - Windows 10 - coverage - **199** seconds
python 3.8.2 - Windows 10 - pytest - 15 seconds
python 3.8.2 - Ubuntu - coverage -  26 seconds
python 3.8.2 - Ubuntu - pytest - 15 seconds
python 3.7.5 - Windows 10 - coverage - **30** seconds
python 3.7.5 - Windows 10 - pytest - 15 seconds
python 3.7.5 - Ubuntu - coverage -  26 seconds
python 3.7.5 - Ubuntu - pytest - 15 seconds

Does anyone have any idea why 3.8 on windows running coverage is so slow?

Answer 1

The cause is that with python 3.8 coverage is installing without C extensions, but with 3.7 it is installing with c extensions.

Now I need to find out why this is the case.