Normalization of equivalent versions

[di]

It'd be nice if there was an easy way to get a "normalized" version, e.g.:

>>> from packaging.version import parse
>>> parse('4.1') == parse('4.1.0')
True
>>> parse('4.1').normalized_version
'4.1.0'

[di]

This is a little complicated by the fact that there can be any number of components in the release segment. Maybe this makes more sense?

>>> parse('4.1').normalize(3)
'4.1.0'
>>> parse('4.1').normalize(5)
'4.1.0.0.0'

I'm not sure I like it.

[dstufft]

Did you mean to close this?

FWIW we have a packaging.utils.canonicalize_name function, so I could see this just being a function like that, which just did something like:

import re
from ..version import parse as parse_version

def canonicalize_version(version):
    # Get the string into it's "Normal" form, but this can still include additional 0s
    version = str(parse_version(version))
    return re.sub(r"^((?:0\.)+)", "", version[::-1])[::-1]

I'd have to go over PEP 440 to be sure, but that should turn any PEP 440 compatible version into a unique string. It obviously wouldn't retain the number of zero's that the package originally had, but if it's not being displayed to users that shouldn't really matter.

[di]

Ah. I got stuck in the rut of thinking only about adding .0s, not removing them. That makes sense.

I'll work on adding this.

[dstufft]

@di I realize my code doesn't really work, since you have to do like 1.0.0.dev0 and stuff to, so it probably needs to understand versions more than my snippet above does. Originally this was how the Version class worked, but I ended up altering it to keep the number of zero's.

The basic idea should still work though, it just might need to either live on the version object so it can get access to the internals to reconstruct it, or you might need to solve #34 so that the canonicalize_version() function can access the parts of a version to munge with the release segment before reconstructing it.

[di]

@dstufft Thanks. I made #125 to address this issue and #34, I'd appreciate your review/merge.