only do this sys.stderr replacing on CPython

diff --git a/Lib/lib2to3/pytree.py b/Lib/lib2to3/pytree.py
index b24283e0eead78144326ab54b055270a819c81f0..c2fa80014a02ec9e3d7fe8f52589fc3b72ac36f0 100644 (file)
--- a/Lib/lib2to3/pytree.py
+++ b/Lib/lib2to3/pytree.py
@@ -743,9 +743,11 @@ class WildcardPattern(BasePattern):
         else:
             # The reason for this is that hitting the recursion limit usually
             # results in some ugly messages about how RuntimeErrors are being
-            # ignored.
-            save_stderr = sys.stderr
-            sys.stderr = StringIO()
+            # ignored. We don't do this on non-CPython implementation because
+            # they don't have this problem.
+            if hasattr(sys, "getrefcount"):
+                save_stderr = sys.stderr
+                sys.stderr = StringIO()
             try:
                 for count, r in self._recursive_matches(nodes, 0):
                     if self.name:
@@ -759,7 +761,8 @@ class WildcardPattern(BasePattern):
                         r[self.name] = nodes[:count]
                     yield count, r
             finally:
-                sys.stderr = save_stderr
+                if hasattr(sys, "getrefcount"):
+                    sys.stderr = save_stderr
 
     def _iterative_matches(self, nodes):
         """Helper to iteratively yield the matches."""