Issue #13521: dict.setdefault() now does only one lookup for the given key, making it "atomic" for many purposes.
Patch by Filip Gruszczyński.
diff --git a/Misc/NEWS b/Misc/NEWS
index 0375ff3..b69eb4b 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@
Core and Builtins
-----------------
+- Issue #13521: dict.setdefault() now does only one lookup for the given key,
+ making it "atomic" for many purposes. Patch by Filip Gruszczyński.
+
- Issue #13703: oCERT-2011-003: add -R command-line option and PYTHONHASHSEED
environment variable, to provide an opt-in way to protect against denial of
service attacks due to hash collisions within the dict and set types. Patch