Python coverage is installing without C extension on Windows under python 3.8, but not under python 3.7, how do I force the C extension version?

Question

I have python 3.7.5 and Python 3.8 installed on the same windows 10 machine. They were both installed from python.org/downloads. When I run pip install coverage (using the latest release of pip) it installs coverage with c extensions under 3.7.5 and without c extensions under 3.8.2.

How can I force coverage to install with c extensions, as the performance is terrible without them?

It appears 3.7.5 downloads: https://files.pythonhosted.org/packages/4b/c7/6b1af1c8806fa047469b19861a3438f9ce785aa41c831c15d676ccaaa726/coverage-5.0.3-cp37-cp37m-win32.whl

where as 3.8.2 downloads: coverage-5.0.3.tar.gz

The later being "without c extensions"

What version did you install? I see that coverage.py has Windows binary wheels available, including for both 3.7 and 3.8 (and even 3.9!), so perhaps just reinstall? — Martijn Pieters
– Martijn Pieters, Commented Feb 28, 2020 at 13:41
Originally I installed using poetry, then I installed using pip. Both installed version 5.0.3. When I did so for 3.7 it installed version 4.5.4 — Andrew Gill
– Andrew Gill, Commented Feb 28, 2020 at 13:45
Try running pip install --force-reinstall --only-binary :all: -v coverage to demand that a binary (wheel) distribution is picked, and let you know, in minute detail, what pip is finding and deciding. — Martijn Pieters
– Martijn Pieters, Commented Feb 28, 2020 at 13:46
Right, 4.5.4 did not have 3.8 wheels, not for Windows anyway. — Martijn Pieters
– Martijn Pieters, Commented Feb 28, 2020 at 13:48
also, running pip install with no switches will not upgrade an already installed older version. If 4.5.x is installed, you won't get the 5.0.x release with a 3.8 wheels. — Martijn Pieters
– Martijn Pieters, Commented Feb 28, 2020 at 13:49

Martijn Pieters · Accepted Answer · 2020-02-28 16:48:40Z

There are no valid coverage wheel for Windows and Python 3.8 at the moment.

The 5.0.3 wheels on PyPI are marked as compatible with cp38-cp38m-win_amd64, so CPython 3.8, with the cp38m ABI variant, for 64-bit Windows.

But, there is no such ABI variant any more. Python 3.8 no longer has a m (--with-pymalloc) binary variant, because builds with or without --with-pymalloc are now ABI compatible.

Pip has followed suit and stopped adding the m flag when looking for wheels, and the wheel project, which creates these distribution files also dropped the m flag.

However, coverage.py is using an older release of wheel to build the distributions, they are using 0.33.1, while the above changes landed in version 0.33.5. You already filed a bug report with the project, I've added my findings there too.

Luckily, the flag is superficial. You can download the wheel file directly from PyPI, rename the file (removing the m from cp38m) and then use pip install path/to/renamed/coverage-5.0.3-cp38-cp38m-win_amd64.whl.

Note: the same issue applies to the 3.9 wheels.

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Python coverage is installing without C extension on Windows under python 3.8, but not under python 3.7, how do I force the C extension version?

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