Python: use PyPI mirror

[FRidh]

Recently PyPI changed their url scheme at https://pypi.python.org. After some complaints they mapped the older urls to the new ones again. This is however done on the upcoming PyPI 2.0 website, and not the current website.

In this PR the new website (https://pypi.io) is added as mirror. The new website works most of the time but can still fail occasionally and is not as reliable as the old one.

cc @domenkozar @wkennington

[mention-bot]

By analyzing the blame information on this pull request, we identified @bjornfor, @matthiasbeyer and @domenkozar to be potential reviewers

[domenkozar]

Travis seems to indicate it's a mass rebuild, I don't understand why. It's changing only fixed output drvs.

[dezgeg]

Seems like nox is comparing drv paths: https://github.com/madjar/nox/blob/master/nox/nixpkgs_repo.py#L80

[domenkozar]

Nice catch! Opened madjar/nox#44

[domenkozar]

I really see no reason to merge this, we'll fix issues as they come or switch to another mirror.

[domenkozar]

Verified using pythonPackages.msgpack and bumped the version.

[grahamc]

My only concern with this is we're now codifying that pypi is the old style pypi URLs. In fact, PyPI has changed their URLs and are only providing these old style redirects as a favor for packagers like us. Given the rest of @FRidh's goals, I think it would be wiser to rename the pypi mirror to pypi-v1 (or whatever) so then we have an easier time moving forward by calling the newer style URLs pypi-v2.

[FRidh]

If we keep in mind that this is not an official API and agree that if it turns out to be unreliable and that we need a better solution by using say the API, then I think it is fine.

I will anyway work further on autogenerated urls and hashes using the API.

[FRidh]

with the pypi-v1 you have a good point, at least, thinking about people that use it outside of buildPythonPackage.