improve pkg_resources.Distribution.hashcmp performance

[gotcha]

by storing location without md5.

Turns Distribution.location into a property to make hashcmp more performant.

Closes #2089

Pull Request Checklist

• Changes have tests
• News fragment added in changelog.d. See documentation for details

[gotcha]

As the fix is not supposed to change any semantics, I wonder which sort of tests should be added.

[jaraco]

Although this approach achieves the desired result (only calculate _location_without_md5 once), it causes quite a bit of entanglement with the location property, unnecessarily adding a new ._location property. How about instead having _location_without_md5 be a cached property or method to avoid it being calculated more than once for any given Distribution?

[gotcha]

I make location a property as there is afaik nothing that avoids setting location twice.

[jaraco]

That's fair, and I had the same concern.

After inspecting the code, it appears it's only ever set once during the constructor. I'd hate to add code that explicitly adds support for setting the value later when it will only ever be set once during construction.

I'll go with #2098 until a use-case demands a setter. Thanks for the contrib!

[jaraco]

I think more important than before accepting either PR will be to define a problem that needs to be solved, so I'll await an answer in #2089

[jaraco]

I prefer #2108. Thanks again for the contrib.

[gotcha]

It is always better to remove code when possible.