formats.pythonVars: init

pkgs/pkgs-lib/formats.nix

@@ -417,4 +417,39 @@ rec {
       '';
     };
 
+  # Outputs a succession of Python variable assignments
+  # Useful for many Django-based services
+  pythonVars = {}: {
+    type = with lib.types; let
+      valueType = nullOr(oneOf [
+        bool
+        float
+        int
+        path
+        str
+        (attrsOf valueType)
+        (listOf valueType)
+      ]) // {
+        description = "Python value";
+      };
+    in attrsOf valueType;
+    generate = name: value: pkgs.callPackage ({ runCommand, python3, black }: runCommand name {
+      nativeBuildInputs = [ python3 black ];
+      value = builtins.toJSON value;
+      pythonGen = ''
+        import json
+        import os
+
+        with open(os.environ["valuePath"], "r") as f:
+            for key, value in json.load(f).items():
+                print(f"{key} = {repr(value)}")
+      '';
+      passAsFile = [ "value" "pythonGen" ];
+    } ''
+      cat "$valuePath"
+      python3 "$pythonGenPath" > $out
+      black $out
+    '') {};
+  };
+
 }