From: Tim Peters <tim.peters@gmail.com>
Date: Sun, 25 Aug 2002 18:59:04 +0000 (+0000)
Subject: Added a clue about why xyz_update isn't the same as __xyz__.
X-Git-Tag: v2.3c1~4291
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=4a2f91e302956ecaa5a70c42b403967e4b261a3d;p=thirdparty%2FPython%2Fcpython.git

Added a clue about why xyz_update isn't the same as __xyz__.
---

diff --git a/Lib/sets.py b/Lib/sets.py
index 3897fb9d7cce..8808701d2447 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."""