Change in cache tag in Python 3.8 - pip confused

[Chris Angelico]

I've been building Python 3.8 pre-alphas and alphas for a while now,
and ran into a weird problem. Not sure if this is significant or not,
and hoping to get other people's views.

It seems that the value of sys.implementation.cache_tag changed from
"cpython-38m" to just "cpython-38" at some point. That means that a
statement like "import lzo" will no longer find a file called
"lzo.cpython-38m-x86_64-linux-gnu.so", which I had had prior to the
change. The trouble is, pip *did* recognize that file, and said that
the python-lzo package was still installed.

Solution: "pip uninstall python-lzo" and then reinstall it. Now it's
created "lzo.cpython-38-x86_64-linux-gnu.so" and all is well.

Does anyone else know about how pip detects existing files, and
whether it could be brought more in sync with the import machinery?

ChrisA