only do this sys.stderr replacing on CPython

1 files changed, 7 insertions, 4 deletions

diff --git a/Lib/lib2to3/pytree.py b/Lib/lib2to3/pytree.py
index b24283e..c2fa800 100644
--- 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."""