We have been using this command to install Python to our container:
RUN pip3 install -U pip && \
    pip install wheel && \
    pip wheel -w /tmp/wheels 

It started failing today with the following error:

ERROR: PyYAML-6.0-cp39-cp39-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_12_x86_64.manylinux2010_x86_64.whl is not a supported wheel on this platform.

It turned out the install now downloads the cp39 wheel: 

12:46:14  Collecting pyyaml>=3.12
12:46:14    Downloading PyYAML-6.0-cp39-cp39-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_12_x86_64.manylinux2010_x86_64.whl (661 kB)


When this worked a couple of days ago, the install downloaded a different wheel:

15:03:12  Collecting pyyaml>=3.12
15:03:12    Downloading PyYAML-6.0-cp36-cp36m-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_12_x86_64.manylinux2010_x86_64.whl (603 kB)


Why does the python install download the cp39 wheel now?

This is the wrong place to report bugs with third party packages or wheels. The Python bug tracker is only for core development. Please use one of the community channels to get assistance, https://www.python.org/community/

Thanks Christian. But why the python installer suddenly started using cp39 of the yaml wheel? It used to be using cp36 of the wheel which was working fine. Trying to gather more information so that I can talk to the 3rd party about this.

This is really a question for pip, which is a third party product (despite a version of it shipping with core python). You can find their issue tracker at https://pip.pypa.io/en/stable/

When reporting the bug there, you'll need to provide information about which python you're using, how you installed it, and which version of pip you're using. And probably also the verbose output from pip.

Thanks Eric. I created an issue in the pip repo.