From e1618491adc5c0ef214c25d4e3b882e8586a2fee Mon Sep 17 00:00:00 2001
From: Antoine Pitrou <solipsis@pitrou.net>
Date: Sat, 4 Oct 2014 22:15:27 +0200
Subject: Issue #21905: Avoid RuntimeError in pickle.whichmodule() when
 sys.modules is mutated while iterating.

Patch by Olivier Grisel.
---
 Lib/pickle.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

(limited to 'Lib/pickle.py')

diff --git a/Lib/pickle.py b/Lib/pickle.py
index 3fc2596e67..663773f3d9 100644
--- a/Lib/pickle.py
+++ b/Lib/pickle.py
@@ -280,7 +280,9 @@ def whichmodule(obj, name, allow_qualname=False):
     module_name = getattr(obj, '__module__', None)
     if module_name is not None:
         return module_name
-    for module_name, module in sys.modules.items():
+    # Protect the iteration by using a list copy of sys.modules against dynamic
+    # modules that trigger imports of other modules upon calls to getattr.
+    for module_name, module in list(sys.modules.items()):
         if module_name == '__main__' or module is None:
             continue
         try:
-- 
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