Issue 7910: immutability w/r to tuple.add (original) (raw)

Issue7910

Created on 2010-02-11 15:26 by mattrussell, last changed 2022-04-11 14:56 by admin. This issue is now closed.

Messages (4)
msg99219 - (view)	Author: Matthew Russell (mattrussell)	Date: 2010-02-11 15:26
Tuples, as we know are designed to immutable. Hence I'm questioning if the following behavior is considered a defect: >>> t = (1, 2) >>> t += (1, 2, 3) >>> t (1, 2, 3) ?
msg99220 - (view)	Author: Jean-Paul Calderone (exarkun) *	Date: 2010-02-11 15:28
Your output looks fishy. Anyway, the behavior of += isn't a bug: >>> a = b = (1, 2) >>> a += (1, 2, 3) >>> a (1, 2, 1, 2, 3) >>> a is b False >>> It's confusing, to be sure, but no mutation is going on. += is only in-place if applied to something that supports mutation this way (by implementing __iadd__).
msg99221 - (view)	Author: Tim Golden (tim.golden) *	Date: 2010-02-11 15:32
Just think about it for a minute: t = (1, 2) print id (t), t t += (1, 2, 3) print id (t), t Not mutating, merely creating a new new object and giving it the same name
msg99225 - (view)	Author: Matthew Russell (mattrussell)	Date: 2010-02-11 15:40
Yes, the output is fishy indeed my bad (paste error). Tim: I hadn't thought for long enough or thought to check with the id builtin - nice catch.