From 7489a2577db03864d93b07e3e8263f2c27bb01ad Mon Sep 17 00:00:00 2001
From: Jonas Rembser <jonas.rembser@cern.ch>
Date: Tue, 12 May 2026 14:17:49 +0200
Subject: [PATCH] [Python] Prevent possible double pythonization of template
 classes

If the current C++ global namespace containts both template
instantiations and the original class template, which can happen
depending on the usage pattern, it can happen that the same template
instance is pythonized twice. This is prevented with additional
conditionals in the pythonization code paths.
---
 .../pythonizations/python/ROOT/_pythonization/__init__.py    | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/bindings/pyroot/pythonizations/python/ROOT/_pythonization/__init__.py b/bindings/pyroot/pythonizations/python/ROOT/_pythonization/__init__.py
index 8907388ecd296..b2ec9c4937273 100644
--- a/bindings/pyroot/pythonizations/python/ROOT/_pythonization/__init__.py
+++ b/bindings/pyroot/pythonizations/python/ROOT/_pythonization/__init__.py
@@ -274,8 +274,9 @@ def get_class_name(instantiation):
 
     ns_vars = vars(ns_obj)
     for var_name, var_value in ns_vars.items():
-        if str(var_value).startswith("<class cppyy.gbl."):
-            # It's a class proxy
+        if str(var_value).startswith("<class cppyy.gbl.") and not hasattr(var_value, "__cpp_template__"):
+            # It's a class proxy. Exclude template instantiations, because they
+            # will be traversed in the next step.
             pythonize_if_match(var_name, var_value)
 
         if str(var_value).startswith("<cppyy.Template"):