From 4a2f91e302956ecaa5a70c42b403967e4b261a3d Mon Sep 17 00:00:00 2001 From: Tim Peters Date: Sun, 25 Aug 2002 18:59:04 +0000 Subject: [PATCH] Added a clue about why xyz_update isn't the same as __xyz__. --- Lib/sets.py | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/Lib/sets.py b/Lib/sets.py index 3897fb9d7cc..8808701d244 100644 --- a/Lib/sets.py +++ b/Lib/sets.py @@ -361,7 +361,10 @@ class Set(BaseSet): # We inherit object.__hash__, so we must deny this explicitly raise TypeError, "Can't hash a Set, only an ImmutableSet." - # In-place union, intersection, differences + # In-place union, intersection, differences. + # Subtle: The xyz_update() functions deliberately return None, + # as do all mutating operations on built-in container types. + # The __xyz__ spellings have to return self, though. def __ior__(self, other): """Update a set with the union of itself and another."""