[issue6017] Dict fails to notice addition and deletion of keys during iteration
Georg Brandl ge...@python.org added the comment: OK, I now changed it to may raise ... or fail to iterate over all entries in r72708. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6017 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6017] Dict fails to notice addition and deletion of keys during iteration
Steven D'Aprano st...@pearwood.info added the comment: I agree with Terry Reedy. I'm re-opening it as a documentation bug (if I can -- if I can't, I'll just request somebody who can do so). -- components: -Interpreter Core status: closed - open ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6017 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6017] Dict fails to notice addition and deletion of keys during iteration
Georg Brandl ge...@python.org added the comment: I don't think it would be better to change the documentation to will raise a RuntimeError or result in undefined behavior. It already tells you not to do this strongly enough. -- status: open - closed ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6017 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6017] Dict fails to notice addition and deletion of keys during iteration
R. David Murray rdmur...@bitdance.com added the comment: The precisionist in me insists that at a minimum 'will' should be changed to 'may'. Otherwise either the docs are lying or the implementation has a bug. Or perhaps we could add a footnote about the intentionally divergent behavior of the CPython implementation? (As Terry pointed out these docs may be used by other implementors as a prescriptive guide, just as the language reference is.) -- nosy: +r.david.murray ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6017 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6017] Dict fails to notice addition and deletion of keys during iteration
Steven D'Aprano st...@pearwood.info added the comment: With respect Georg, given that the behaviour won't be changed, the documentation is simply *wrong*. It's not a matter of telling people don't do this -- somebody, somewhere, is going to rely on the documented behaviour. The docs make the clear promise that, and I quote, Using iteritems() while adding or deleting entries in the dictionary will raise a RuntimeError, but that's not what happens. The actual behaviour is undefined. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6017 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6017] Dict fails to notice addition and deletion of keys during iteration
Georg Brandl ge...@python.org added the comment: I wouldn't call it *wrong* as much as *not the whole truth*. It is true that if just one key is added or removed, a RuntimeError will be raised. There are probably lots of places in our docs where the whole truth isn't told, but in a way that works if you do the sensible thing. In this case I can neither see anyone relying on RuntimeError being raised (except for dict's own test suite), nor an implementor looking only at these docs, not the source, to implement one of Python's most crucial object types. Anyway, if you find a new wording that isn't too clumsy, I'll change it. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6017 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6017] Dict fails to notice addition and deletion of keys during iteration
Terry J. Reedy tjre...@udel.edu added the comment: I would be happy enough to change 'will' to 'may'. There are a lot of undocumented exception-raising circumstances, and this one already be undocumented in Py3. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6017 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6017] Dict fails to notice addition and deletion of keys during iteration
Terry J. Reedy tjre...@udel.edu added the comment: The OP reported a real mismatch between doc and behavior. If the behavior is not changed, I think the doc should be. Other implementors, reading the doc, might think that they do have to write code to track changes. From the doc, I thought that CPython did that. So I suggest changing reopening and changing the doc to say Changing the net size of the dictionary while using iteritems() will raise a RuntimeError. Same for iterkeys() and itervalues()[sp?] Or remove the warning, as happened in the Py3 changeover to views, or was that a mistake? -- nosy: +tjreedy ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6017 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6017] Dict fails to notice addition and deletion of keys during iteration
Benjamin Peterson benja...@python.org added the comment: This is correct; dict iterators check to see if the size of the dict is different. However, fixing this problem would require tracking dict contents during iteration. That strikes me as too inefficient and too much code for this little case. -- nosy: +benjamin.peterson resolution: - wont fix status: open - closed ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6017 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6017] Dict fails to notice addition and deletion of keys during iteration
New submission from Steven D'Aprano st...@pearwood.info:
I'm not sure if this is a documentation bug or a behaviour bug, or
possibly both.
The documentation warns about adding or deleting items from a dict
while iterating over it:
Using iteritems() while adding or deleting entries in the dictionary
will raise a RuntimeError.
http://docs.python.org/library/stdtypes.html#dict.iteritems
Same for other dict iterators.
However, you can add and delete items, so long as the overall size of
the dict doesn't change. Consequently, some modifications to the dict
aren't caught, leading to various misbehaviour in (at least) Python
2.5 and 2.6.
Some dicts appear to run too long:
d = dict(x=3, y=4) # Two items
it = d.iteritems()
it.next() # One
('y', 4)
del d['y']
d['z'] = 5
it.next() # Two
('x', 3)
it.next() # Three
('z', 5)
While others run too short:
d = {-1: 'aa', -2: 'bb'} # Two items
it = d.iteritems()
it.next() # One
(-2, 'bb')
del d[-1]
d[0] = 'cc'
it.next()
Traceback (most recent call last):
File stdin, line 1, in module
StopIteration
--
assignee: georg.brandl
components: Documentation, Interpreter Core
messages: 87729
nosy: georg.brandl, stevenjd
severity: normal
status: open
title: Dict fails to notice addition and deletion of keys during iteration
type: behavior
versions: Python 2.5, Python 2.6
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