python3Packages.mmcv: fix on python 3.13

pkgs/development/python-modules/mmcv/default.nix

@@ -48,10 +48,17 @@ buildPythonPackage rec {
     hash = "sha256-NNF9sLJWV1q6uBE73LUW4UWwYm4TBMTBJjJkFArBmsc=";
   };
 
-  postPatch = ''
-    substituteInPlace setup.py \
-      --replace-fail "cpu_use = 4" "cpu_use = $NIX_BUILD_CORES"
-  '';
+  postPatch =
+    # Fails in python >= 3.13
+    # exec(compile(f.read(), version_file, "exec")) does not populate the locals() namesp
+    # In python 3.13, the locals() dictionary in a function does not automatically update with
+    # changes made by exec().
+    # https://peps.python.org/pep-0558/
+    ''
+      substituteInPlace setup.py \
+        --replace-fail "cpu_use = 4" "cpu_use = $NIX_BUILD_CORES" \
+        --replace-fail "return locals()['__version__']" "return '${version}'"
+    '';
 
   nativeBuildInputs = [
     ninja