getting flake to work

flake.nix

@@ -1,21 +1,51 @@
 {
-  description = "Python dev environment using Nix";
+  description = "A development shell for Python 3.12 with Pandas and Requests.";
 
-  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.05";
-
-  outputs = { self, nixpkgs }: let
-    system = "x86_64-linux";
-    pkgs = import nixpkgs { inherit system; };
-  in {
-    devShells.${system}.default = pkgs.mkShell {
-      packages = [
-        (pkgs.python312.withPackages (ps: with ps; [
-          pip
-          virtualenv
-          black
-          pytest
-        ]))
-      ];
-    };
+  # Define the inputs (dependencies) for the flake
+  inputs = {
+    # Pin nixpkgs to a specific channel (e.g., nixos-unstable) for a reproducible environment
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
   };
+
+  # Define the outputs (what the flake provides)
+  outputs = { self, nixpkgs, ... }@inputs:
+    let
+      # Define the systems this flake supports
+      supportedSystems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
+
+      # Create a function that maps the supported systems to the nixpkgs instance
+      forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
+
+      # Get the packages set for all systems
+      pkgs = forAllSystems (system: import nixpkgs { inherit system; });
+
+    in
+    {
+      # Define the development shells
+      devShells = forAllSystems (system: {
+        default = pkgs.${system}.mkShell {
+          name = "python-312-dev-shell";
+
+          # 1. Select the specific Python interpreter (Python 3.12)
+          # 2. Use .withPackages to create an environment that includes the specified libraries
+          packages = [
+            (pkgs.${system}.python312.withPackages (python-pkgs: with python-pkgs; [
+              # Python libraries
+              pandas
+              requests
+
+              # Optional: Add other helpful dev tools outside of the python-pkgs set if needed
+              # (e.g., git, pre-commit, bash-completion)
+            ]))
+          ];
+
+          # Optional: Define environment variables for the shell
+          shellHook = ''
+            echo "🐍 Entering Python 3.12 development environment."
+            echo "   (Pandas and Requests are available)"
+            python --version
+          '';
+        };
+      });
+    };
 }