> PEP 425 explicitly covers that.

It says "The version is py_version_nodot. CPython gets away with no dot, but if one is needed the underscore _ is used instead. PyPy should probably use its own versions here pp18, pp19".

The "probably" leaves some room for doubt as to what exactly is meant: both wheel and distlib use py_version_nodot, and the last sentence I quoted looks provisional rather than definitive.

Regards,

Vinay Sajip