Dependency resolution can't handle PEP 503-style normalized package names

[nikhaldi]

PyPI and setuptools support package name normalization as per PEP 503: https://www.python.org/dev/peps/pep-0503/#normalized-names

This means that a package like https://pypi.org/project/pytest-selenium/ can be installed both with pip install pytest.selenium and pip install pytest-selenium.

pex only accepts already normalized package names. If I put pytest.selenium in a requirements.txt file this won't work:

$ pex -o pex.bin -vvvv -r requirements.txt 
pex: Constructed RequestsContext context <pex.http.RequestsContext object at 0x107466910>
pex: Constructed RequestsContext context <pex.http.RequestsContext object at 0x10701c950>
pex: crawling link i=0 link=Link('file:///Users/nik/.pex/build') follow_links=False
pex: crawling link i=0 link=Link('https://pypi.org/simple/pytest-selenium/') follow_links=False
Could not satisfy all requirements for pytest.selenium:
    pytest.selenium

Same works with pytest-selenium.

For consistency with other build tools pex should support this as well. Arguably the PEP 503 behavior is weird (I only just learned about it today too) and probably bad design. But consistency across tools might trump bad design decisions. I came across this because a user was trying an existing requirements file that had always worked for them with pip and couldn't figure out why it failed in pex.

[jsirois]

Thanks for pointing this out @nikhaldi - I agree we should support this.