Comment on the set_swap_bodies() helper function.
diff --git a/Objects/setobject.c b/Objects/setobject.c
index e922b6e..a279ec2 100644
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -793,6 +793,19 @@
return ((PySetObject *)so)->used;
}
+/* set_swap_bodies() switches the contents of any two sets by moving their
+ internal data pointers and, if needed, copying the internal smalltables.
+ Semantically equivalent to:
+
+ t=set(a); a.clear(); a.update(b); b.clear(); b.update(t); del t
+
+ The function always succeeds and it leaves both objects in a stable state.
+ Useful for creating temporary frozensets from sets for membership testing
+ in __contains__(), discard(), and remove(). Also useful for operations
+ that update in-place (by allowing an intermediate result to be swapped
+ into one of original the inputs).
+*/
+
static void
set_swap_bodies(PySetObject *a, PySetObject *b)
{