Python on macOS is built against 10.14 SDK

[rdb]

It looks like the Python interpreters on macOS are compiled with macOS 10.14 as deployment target. They should rather be built against the oldest supported macOS SDK so that no errors are encountered when a program built against an older SDK is linked with the Python libraries. (Ideally we'd like to build against the 10.9 SDK, but unfortunately it is not supported; it will have to be 10.12, I suppose.)

[letmaik]

I can confirm that. A good reference of what viable deployment target versions should be can be seen from what's available from python.org: https://www.python.org/ftp/python/3.7.4/ There we have 10.6 and 10.9. Note for 3.5 there is only 10.5 and 10.6. It seems like the recommended approach is to use 10.6 for 3.5 and 10.9 for >3.5.
Due to this I'm currently forced to install Python manually in order to generate binary wheels that are widely compatible.
For reference, the deployment target can be influenced by setting the MACOSX_DEPLOYMENT_TARGET environment variable.

[letmaik]

Addition: I don't think SDK is strictly linked to deployment target. I was able to set MACOSX_DEPLOYMENT_TARGET=10.9 and together with the Python from python.org I could build 3.6 and 3.7 wheels which have the 10.9 platform tag. I'm not a macOS expert, so maybe someone else can make sense of that. Maybe a certain SDK supports multiple deployment targets (same and older up to some lower bound)?

[coldfix]

Note that while the situation remains as is, a workaround for users is to replace actions/setup-python by setting up conda environments, e.g.:

      - uses: goanpeca/setup-miniconda@v1
        with:
          architecture: x64
          python-version: '3.8'
          # must be explicitly specified if architecture is not x64:
          miniconda-version: latest

      - run: |
          conda create -qyf py35 python=3.5 wheel -c anaconda
          conda activate py35
          python setup.py sdist bdist_wheel
        shell: bash -l {0}

      - run: |
          conda create -qyf py36 python=3.6 wheel -c anaconda
          conda activate py36
          python setup.py sdist bdist_wheel
        shell: bash -l {0}

      ...

which will result in the following deployment targets:

• py2.7: 10.7
• py3.5: 10.6
• py3.6: 10.9
• py3.7: 10.9
• py3.8: 10.9

[dmitry-shibanov]

Hello everyone. I'm going to close the feature request because we do not provide macOS with older versions and we're not planing to build python against of 10.9.

[rdb]

Why? This is a trivial change to make, and means setup-python will be useful to those who want to keep targeting 10.9.

The version of macOS (or the SDK) you provide is irrelevant to the deployment target you set when building Python.