Define pkg as a PackageURL class attribute

[jaimergp]

This will allow library users to subclass PackageURL and redefine the scheme to create PURL-like derivatives. (e.g. for the dep: idea described here):

class DependencyURL(PackageURL):
    SCHEME = "dep"

Which can be used in the same way and happily accepts PEP440-like version ranges in the version field 🥳:

>>> dep = DependencyURL.from_string("dep:pypi/requests@>=2.0")
>>> dep
DependencyURL(type='pypi', namespace=None, name='requests', version='>=2.0', qualifiers={}, subpath=None)

[pombredanne]

@jaimergp this is fine by me BTW... no objections to make it easier to reuse!

[pombredanne]

Ah, I see, this is now with #186

[jaimergp]

Ah, @pombredanne, if you are fine with this type of change, yes, please, let's reopen!

[jaimergp]

@pombredanne (or anyone with merge rights!) gentle ping for a hopefully uncontroversial review!

[tdruez]

I'm wondering if using lower-caps scheme for consistency with existing vars would make more sense. I don't see anything declared as upper-caps in that module.

[jaimergp]

I used uppercase because it's supposed to be constant for the class, maybe I can indicate that with ClassVar[str] instead.

[jaimergp]

Changed to ClassVar[str]

[jaimergp]

Thanks @tdruez, let me know if I addressed your concerns!

[tdruez]

@jaimergp Thanks! LGTM.

@pombredanne Could you give it another look and take care of the merge?

[pombredanne]

All fine! Thanks!