[3.6] bpo-30441: Fix bug when modifying os.environ while iterating over it (GH-2409). (#2556)

(cherry picked from commit 8a8d28501fc8ce25926d168f1c657656c809fd4c)

1 files changed, 3 insertions, 1 deletions

diff --git a/Lib/os.py b/Lib/os.py
index fa06f39..9fa8acb 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -685,7 +685,9 @@ class _Environ(MutableMapping):
             raise KeyError(key) from None
 
     def __iter__(self):
-        for key in self._data:
+        # list() from dict object is an atomic operation
+        keys = list(self._data)
+        for key in keys:
             yield self.decodekey(key)
 
     def __len__(self):