Why is the nix-compiled Python slower?

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10

Here’s an example default.nix that you can put in your project and use nix-shell.

{ nixpkgs ? (builtins.fetchTarball {
    url = "https://github.com/NixOS/nixpkgs/archive/ba02fd0434ed92b7335f17c97af689b9db1413e0.tar.gz";
    sha256 = "1pjx78qb3k4cjkbwiw9v0wd545h48fj4criazijwds53l0q4dzn1";
  })
, src ? builtins.fetchGit ./.
}:
let
  pkgs = import nixpkgs { };
  python38Optimized = pkgs.python38.override {
    enableOptimizations = true;
    reproducibleBuild = false;
    self = python38Optimized;
  };
  pyPkgs = python38Optimized.pkgs;
in
python38Optimized.pkgs.buildPythonPackage rec {
  name = "python-example";
  inherit src;
  propagatedBuildInputs = with pyPkgs; [
    numpy
  ];
  nativeBuildInputs = with pyPkgs; pkgs.lib.optionals (pkgs.lib.inNixShell) [
    ipython
  ];
}

Notes:

  • The expression requires the directory to be versioned with git
  • Fetch a hot beverage while it compiles Python 3.8 for you on the first launch
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