[Python-bugs-list] [ python-Bugs-475678 ] y += x versus y = y+x surprise (original) (raw)

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Sat, 27 Oct 2001 20:22:48 -0700

Bugs item #475678, was opened at 2001-10-27 20:22 You can respond by visiting: http://sourceforge.net/tracker/?func=detail&atid=105470&aid=475678&group_id=5470

Category: Python Interpreter Core Group: None Status: Open Resolution: None Priority: 7 Submitted By: Tim Peters (tim_one) Assigned to: Nobody/Anonymous (nobody) Summary: y += x versus y = y+x surprise

Initial Comment: This report from c.l.py. At a PythonLabs release mtg we agreed it was "a bug". Offhand, though, I don't recall which part was considered buggy <wink/sigh>.

""" From: Dale Strickland-Clark Sent: Monday, October 22, 2001 6:20 PM To: python-list@python.org Subject: Augmented augmented assignment?

Can someone explain this?

It doesn't seem obvious to me but it's quite handy.

I assume it's something to do with the in-place operation of augmented assignment but I can't seem to reproduce it using normal assignment.

x = 'spam' y = [] y = y + x Traceback (most recent call last): File "", line 1, in ? TypeError: can only concatenate list (not "string") to list y += x y ['s', 'p', 'a', 'm'] """

Note that both behaviors were in 2.0, so

a. This isn't due to "iterable object" generalization (it's due to list += mapping to list.extend).

and

b. There are backward-compatibility concerns.

You can respond by visiting: http://sourceforge.net/tracker/?func=detail&atid=105470&aid=475678&group_id=5470