Python support for pyyaml 5.4

[brews]

Problem description

The Python pulumi SDK and pulumi-kubernetes have different/incompatible restrictions on the pyyaml dependency.

pulumi-kubernetes supports 'pyyaml>=5.3.1,<5.4' but pyyaml 5.4 was released a few hours ago.The trouble is the pulumi Python SDK only requires 'pyyaml>=5.3.1'. So, when setting up the environment as part of a CI/CD job, for example, pip installs pyyaml 5.4 and pulumi itself then chokes on the incompatible pulumi-kubernetes and pyyaml versions when starting a preview.

Relevant lines from error logs are:

...
      File "/builds/fakeproject/venv/lib/python3.8/site-packages/pkg_resources/__init__.py", line 792, in resolve
        raise VersionConflict(dist, req).with_context(dependent_req)
    pkg_resources.ContextualVersionConflict: (PyYAML 5.4 (/builds/fakeproject/venv/lib/python3.8/site-packages), Requirement.parse('pyyaml<5.4,>=5.3.1'), {'pulumi-kubernetes'})
    error: an unhandled error occurred: Program exited with non-zero exit code: 1

This got burned because setuptools and the package constraints in setup.py are not used to test or resolve conflicting dependencies in an environment.

Suggestions for a fix

Remove or extend the cap on pyyaml<5.4 in pulumi-kubernetes's setup.py, if possible.

My workaround has been to add pyyaml=5.3.* to requirements.txt, though it is not really a direct dependency.