New submission from Serhiy Storchaka:
Currently dict iterating is guarded against changing dict's size. However when
dict changed during iteration so that it's size left unchanged, this
modification left unnoticed.
>>> d = dict.fromkeys('abcd')
>>> for i in d:
... print(i)
... d[i + 'x'] = None
... del d[i]
...
d
a
dx
dxx
ax
c
b
In general iterating over mutating dict considered logical error. It is good
detect it as early as possible.
The proposed patch introduces a counter which changed every time when added or
removed key. If an iterator detects that this counter is changed, it raises
runtime error.
----------
components: Interpreter Core
files: dict_mutating_iteration.patch
keywords: patch
messages: 200784
nosy: pitrou, rhettinger, serhiy.storchaka
priority: normal
severity: normal
stage: patch review
status: open
title: Guard against changing dict during iteration
type: enhancement
versions: Python 3.4
Added file: http://bugs.python.org/file32279/dict_mutating_iteration.patch
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<http://bugs.python.org/issue19332>
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