[issue24369] Using OrderedDict.move_to_end during iteration is problematic.
Eric Snow added the comment: Here's a patch that tracks changes to the C OrderedDict linked list, similar to how it's done in deque. I've left the pure Python OrderedDict alone. @Raymond, that state counter works great. :) -- keywords: +patch stage: test needed - patch review Added file: http://bugs.python.org/file39610/issue24369-iteration-mutation.diff ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue24369 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue24369] Using OrderedDict.move_to_end during iteration is problematic.
New submission from Eric Snow:
While the dict/OrderedDict iterators already check for additions and deletions,
using the OrderedDict.move_to_end during iteration can lead to surprising
results.
The following results in an infinite loop:
od = OrderedDict.fromkeys('abc')
last = None
for k in od:
if last is not None:
od.move_to_end(last)
last = k
Ideally we could disallow changing order during iteration, just like we
disallow deletion. Since we've gone 3 minor versions already, would it be too
late to break backward compatibility on this point?
--
components: Library (Lib)
messages: 244718
nosy: eric.snow, rhettinger
priority: high
severity: normal
stage: test needed
status: open
title: Using OrderedDict.move_to_end during iteration is problematic.
type: behavior
versions: Python 3.4, Python 3.5, Python 3.6
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[issue24369] Using OrderedDict.move_to_end during iteration is problematic.
Raymond Hettinger added the comment:
The C version should defend itself against any key-changes during iteration
(see the state counter used in deque objects for an example of how to do this).
The pure python version of OrderedDict has only minimal defenses against
mutating during iteration, and it should be left as-is.
FWIW, surprising is in the eye of the beholder. When it comes to mutating
containers during iteration, all kinds of things can happen (that is why
databases implement reader and writer locks).
The following results in an infinite loop:
s = list('abc')
for k in s:
s.append(k)
--
assignee: - rhettinger
priority: high - normal
versions: -Python 3.4
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[issue24369] Using OrderedDict.move_to_end during iteration is problematic.
Eric Snow added the comment: Sounds good. Thanks, Raymond. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue24369 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
