[New-bugs-announce] [issue24369] Using OrderedDict.move_to_end during iteration is problematic.

[Eric Snow]

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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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue24369>
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