made it modular

flake.nix

@@ -1,5 +1,5 @@
 {
-  description = "Reusable Python development environment";
+  description = "Customizable Python development environment";
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
@@ -8,67 +8,121 @@
 
   outputs = { self, nixpkgs, flake-utils }:
     flake-utils.lib.eachDefaultSystem (system:
+      let
+        # Function to create a Python environment with a given version
+        mkPython = { 
+          pythonVersion ? "python313",  # Default Python version
+          extraPackages ? [], # Additional packages to include
+          extraSystemPackages ? [] # Additional system packages
+        }:
         let
           pkgs = import nixpkgs { inherit system; };
           
-        # Python version configuration - easy to change in one place
-        pythonVersion = pkgs.python311;
+          # Select Python version based on the parameter
+          python = pkgs.${pythonVersion};
           
-        # Define Python packages in a separate variable for clarity
-        pythonPackages = ps: with ps; [
+          # Base Python packages that are always included
+          basePackages = ps: with ps; [
             # Data science
             numpy
             pandas
             matplotlib
-          scipy
-          
-          # Web and networking
-          requests
-          httpx
-          beautifulsoup4
             
             # Development tools
             black
-          pylint
             pytest
             ipython
             
-          # Add more packages as needed
+            # Add more default packages as needed
           ];
           
-        # Create the Python environment with the specified packages
-        pythonEnv = pythonVersion.withPackages pythonPackages;
+          # Combine base packages with extra packages
+          allPackages = ps: (basePackages ps) ++ (extraPackages ps);
+          
+          # Create the Python environment
+          pythonEnv = python.withPackages allPackages;
         in
           {
-        # Development shell for interactive use
-        devShells.default = pkgs.mkShell {
+            # The Python environment
+            package = pythonEnv;
+            
+            # Make the chosen Python version accessible
+            inherit python pythonVersion;
+            
+            # Development shell with the Python environment
+            devShell = pkgs.mkShell {
               buildInputs = [
                 pythonEnv
-            pkgs.poetry
-            pkgs.git
-          ];
+              ] ++ extraSystemPackages;
               
               shellHook = ''
-            echo "━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━"
-            echo "🐍 Python $(${pythonVersion}/bin/python --version)"
-            echo "📦 Poetry $(${pkgs.poetry}/bin/poetry --version)"
-            echo "📂 Working directory: $(pwd)"
-            echo "━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━"
+                echo "Python $(${python}/bin/python --version)"
+                echo "Custom Python environment activated!"
               '';
             };
-        
-        # Make the Python environment available as a package
-        packages.default = pythonEnv;
-        
-        # Add an app that runs Python directly
-        apps.default = flake-utils.lib.mkApp {
-          drv = pythonEnv;
-          name = "python";
-          exePath = "/bin/python";
           };
           
-        # Add formatter for consistent Nix code formatting
-        formatter = pkgs.nixpkgs-fmt;
+        # Default Python configuration
+        defaultPython = mkPython {};
+      in
+      {
+        # Expose the function to create custom Python environments
+        lib = {
+          inherit mkPython;
+        };
+        
+        # Default packages using default Python version
+        packages = {
+          default = defaultPython.package;
+        };
+        
+        # Default development shell
+        devShells.default = defaultPython.devShell;
+        
+        # NixOS module for system-wide integration
+        nixosModules.default = { config, lib, pkgs, ... }:
+          with lib;
+          let 
+            cfg = config.services.customPython;
+          in {
+            options.services.customPython = {
+              enable = mkEnableOption "Enable the custom Python environment";
+              
+              pythonVersion = mkOption {
+                type = types.str;
+                default = "python311";
+                description = "Python version to use (e.g., python39, python310, python311)";
+              };
+              
+              extraPackages = mkOption {
+                type = types.functionTo (types.listOf types.anything);
+                default = _: [];
+                description = "Extra Python packages to include";
+              };
+              
+              extraSystemPackages = mkOption {
+                type = types.listOf types.package;
+                default = [];
+                description = "Extra system packages to include";
+              };
+              
+              includeInSystemPackages = mkOption {
+                type = types.bool;
+                default = true;
+                description = "Whether to include the Python environment in system packages";
+              };
+            };
+            
+            config = mkIf cfg.enable {
+              environment.systemPackages = mkIf cfg.includeInSystemPackages [
+                (mkPython {
+                  pythonVersion = cfg.pythonVersion;
+                  extraPackages = cfg.extraPackages;
+                  extraSystemPackages = cfg.extraSystemPackages;
+                }).package
+              ];
+            };
+          };
       }
     );
 }