I would also like to point out that I submitted a patch related to
that a couple of months ago in:
http://bugs.python.org/issue839159
But it never got any attention :( I'm not sure if it is still relevant.
Virgil
On 13-Sep-08, at 10:20 PM, Armin Ronacher wrote:
Hi everybody,
In Python 2.x when iterating over a weak key dictionary for example,
the common
idom for doing that was calling dictionary.keys() to ensure that a
list of all
objects is returned it was safe to iterate over as a weak reference
could stop
existing during dict iteration which of course raises a runtime
error by the
dict iterator.
This was documented behavior and worked pretty well, with the small
problem that
suddenly all references in the dict wouldn't die until iteration is
over because
the list holds references to the object.
This no longer works in Python 3 because .keys() on the weak key
dictionary
returns a generator over the key view of the internal dict which of
course has
the same problem as iterkeys in Python 2.x.
The following code shows the problem::
from weakref import WeakKeyDictionary
f1 = Foo()
f2 = Foo()
d = WeakKeyDictionary()
d[f1] = 42
d[f2] = 23
i = iter(d.keys()) # or use d.keyrefs() here which has the same
problem
print(next(i))
del f2
print(next(i))
This example essentially dies with "RuntimeError: dictionary changed
size during iteration" as soon as f2 is deleted.
Iterating over weak key dictionaries might not be the most common
task but I
know some situations where this is necessary. Unfortunately I can't
see a
way to achieve that in Python 3.
Regards,
Armin
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