如何在Nix Flake中为对应系统选择合适的Python版本？

现有flake.nix配置如下：

{
  description = "EMR Serverless compatible Python env";

  # Flake inputs
  inputs = {
    nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.2405.*.tar.gz";
    nixpkgs-python.url = "github:cachix/nixpkgs-python";
  };

  # Flake outputs
  outputs = { self, nixpkgs, nixpkgs-python }:
    let
      # Systems supported
      allSystems = [
        "x86_64-linux" # 64-bit Intel/AMD Linux
        "aarch64-linux" # 64-bit ARM Linux
        "x86_64-darwin" # 64-bit Intel macOS
        "aarch64-darwin" # 64-bit ARM macOS
      ];

      # Helper to provide system-specific attributes
      forAllSystems = f: nixpkgs.lib.genAttrs allSystems (system: f {
        pkgs = import nixpkgs { inherit system; };
      });
    in
    {
      # Development environment output
      devShells = forAllSystems ({ pkgs }: {
        default =
          let
            python = nixpkgs-python.packages.x86_64-linux."3.9.16";
          in
          pkgs.mkShell {
            # The Nix packages provided in the environment
            packages = [
              # Python plus helper tools
              (python.withPackages (ps: with ps; [
                virtualenv # Virtualenv
                pip # The pip installer
              ]))
            ];
          };
      });
    };

当前配置中，Python版本被硬编码固定为x86_64-linux平台：

python = nixpkgs-python.packages.x86_64-linux."3.9.16";

要实现基于system变量的跨平台适配，只需修改两处：

1. 在forAllSystems的参数传递中加入system变量
2. 用动态的系统标识替代硬编码的平台名称

修改后的完整配置：

{
  description = "EMR Serverless compatible Python env";

  # Flake inputs
  inputs = {
    nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.2405.*.tar.gz";
    nixpkgs-python.url = "github:cachix/nixpkgs-python";
  };

  # Flake outputs
  outputs = { self, nixpkgs, nixpkgs-python }:
    let
      # Systems supported
      allSystems = [
        "x86_64-linux" # 64-bit Intel/AMD Linux
        "aarch64-linux" # 64-bit ARM Linux
        "x86_64-darwin" # 64-bit Intel macOS
        "aarch64-darwin" # 64-bit ARM macOS
      ];

      # Helper to provide system-specific attributes
      forAllSystems = f: nixpkgs.lib.genAttrs allSystems (system: f {
        pkgs = import nixpkgs { inherit system; };
        inherit system; # 将当前系统标识传入配置函数
      });
    in
    {
      # Development environment output
      devShells = forAllSystems ({ pkgs, system }: { # 接收system变量
        default =
          let
            # 动态获取对应系统的Python 3.9.16包
            python = nixpkgs-python.packages.${system}."3.9.16";
          in
          pkgs.mkShell {
            # The Nix packages provided in the environment
            packages = [
              # Python plus helper tools
              (python.withPackages (ps: with ps; [
                virtualenv # Virtualenv
                pip # The pip installer
              ]))
            ];
          };
      });
    };

关键修改说明：

• 通过inherit system;把当前系统标识传递给每个系统的配置上下文
• 在配置函数中接收system变量，用于动态选择对应平台的Python包
• 替换硬编码的x86_64-linux为${system}，实现跨平台自动适配

内容的提问来源于stack exchange，提问作者sdgfsdh