pythonPackages.fetchpypi: fetch tarballs from pypi

[FRidh]

Things done

• Tested using sandboxing
  (nix.useSandbox on NixOS,
  or option build-use-sandbox in nix.conf
  on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • Linux
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

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This function grabs the url, version and hash for a specified package from a file that was generated by update-hashes.

[FRidh]

Until we have fetchTarball with sha256 support I would like to use this script to update the hashes of the packages.

I could integrate it into the buildPythonPackage function, but what that function needs first is a version parameter, and converting all packages to use that is going to take time.

[FRidh]

We can get rid of the urls by relying on the translator.

[Mic92]

I found buildPyPIPackage cool, because it can set meta, name and version attributes on its own.
Is there a reason for not using this approach?

[Mic92]

How about?

in pname: with data.${pname}; fetchurl { inherit url sha256; meta.version = version;}

I'm not sure, but it could probably make a difference in performance, when the hash lookup only have to be done once.

[FRidh]

@Mic92 thanks for the review.

As I wrote in #16005 we cannot use an external repo yet, because nix stable doesn't yet have fetchTarball with hash support. Even so, we could use the method with buildPyPIPackage and instead keep the json in this repo, like I do in this PR. I'm going to work on that approach, because that's in the direction we will go eventually anyway. The method I use here is also not so convenient for NixOS stable.