Setting / Aliasing the default python versions

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From two reddit posts:

=================

Hello!

As in the title; I’m trying to use the following overlay, but any overlays to python packages I make are not being reflected in the final overlay:

(final: prev: let
    pv2 = "python27";
    pv3 = "python310";
in {
    python2 = final.${pv2};
    python2Packages = final.${pv2}.pkgs;
    python3 = final.${pv3};
    python3Packages = final.${pv3}.pkgs;
    python = final.python3;
    pythonPackages = final.python3.pkgs;
})

I’ve heard that you need to modify python${version}.pkgs manually as well…?

I want to be able to simply use pkgs.python without having to worry about the version every single time.

Thank you kindly for the help!

=================

Hello!

As a followup to my last post here, I was wondering why the following overlays don’t seem to work, as adapted from here, and here:

(final: prev: with final; let
  # Removing recurseForDerivation prevents derivations of aliased attribute set
  # to appear while listing all the packages available.
  removeRecurseForDerivations = alias: with lib;
    if alias.recurseForDerivations or false
    then removeAttrs alias ["recurseForDerivations"]
    else alias;

  # Disabling distribution prevents top-level aliases for non-recursed package
  # sets from building on Hydra.
  removeDistribute = alias: with lib;
    if isDerivation alias then
      dontDistribute alias
    else alias;

  # Make sure that we are not shadowing something from all-packages.nix.
  checkInPkgs = n: alias:
    if builtins.hasAttr n super
    then throw "Alias ${n} is still in all-packages.nix"
    else alias;

  mapAliases = aliases:
    lib.mapAttrs (n: alias:
      removeDistribute
        (removeRecurseForDerivations
          (checkInPkgs n alias)))
      aliases;
in mapAliases {
    python = python3; # Added 2022-01-11
})
(final: prev: {
    # Python interpreters. All standard library modules are included except for tkinter, which is
    # available as `pythonPackages.tkinter` and can be used as any other Python package.
    # When switching these sets, please update docs at ../../doc/languages-frameworks/python.md
    python2 = final.python27;
    python3 = final.python310;

    # pythonPackages further below, but assigned here because they need to be in sync
    python2Packages = dontRecurseIntoAttrs final.python27Packages;
    python3Packages = dontRecurseIntoAttrs final.python310Packages;
})

Thank you kindly for the help!