I don't understand how this is any different.

I believe what you want is to first separate release from the NVR, then split the release by '.'

release = subject_identifier.rsplit('-', 2)[-1]
if '.' not in release:
  return None
short_prod_version = release.split('.')[-1]
return _guess_product_version(short_prod_version, koji_build=True)

Updated.

Please provide some (obfuscated) real-world examples where it would fail, if you know any.

Can we avoid to set the product_version to None? Can't we use "*" or something like that?
None really seems an error/bug. Someone in the team in the past came to me asking me "why I see None in the logs? It's a bug!"

Can we avoid to set the product_version to None?

@gnaponie How about PR#453?

oh, why "_"? :( can we use a more meaningful "term"?

beside one comment, it looks good! Even though... conflicts need to be resolved.

'_' is used as a "don't care" variable name. In this case, the split should produce 3 items, and only the one is interesting. Although the line above could be identical to:

release = subject_identifier.rsplit('-', 2)[-1]

Oh I see. Didn't know that. In this case, either options are fine.
@lholecek the PR looks fine. Once resolved the conflict I think is good to go.

Resolved the conflicts. @lucarval Can you review again pls?

'_' is used as a "don't care" variable name. In this case, the split should produce 3 items, and only the one is interesting. Although the line above could be identical to:
release = subject_identifier.rsplit('-', 2)[-1]

BTW, this is not the same as "tuple unpacking".

>>> a, b, c = 'a-b'.rsplit('-', 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: not enough values to unpack (expected 3, got 2)

But the following doesn't ensure that there are three components.

>>> c = 'a-b'.rsplit('-', 2)[-1]
>>> c
'b'

:+1: