Peter Otten wrote:
> Laszlo Nagy wrote:
>
>> Given this iterator:
>>
>> class SomeIterableObject(object):
>> ....
>> ....
>>
>> def __iter__(self):
>> ukeys = self.updates.keys()
>> for key in ukeys:
>> if self.updates.has_key(key):
Hm, I see you are using has_key() which is 2.x-only and invalidates my
explanation :(
>> yield self.updates[key]
>> for rec in self.inserts:
>> yield rec
>> ....
>> ....
>>
>> How can I get this exception:
>>
>> RuntimeError: dictionary changed size during iteration
>>
>>
>> It is true that self.updates is being changed during the iteration. But
>> I have created the "ukeys" variable solely to prevent this kind of
>> error. Here is a proof of correctness:
>>
>>>>> d = {1:1,2:2}
>>>>> k = d.keys()
>>>>> del d[1]
>>>>> k
>> [1, 2]
>>>>> k is d.keys()
>> False
>>
>> So what is wrong with this iterator? Why am I getting this error message?
>
> The keys() method which used to return a list in 2.x was changed in 3.x to
> return a view object and to become more or less the equivalent of the old
> dict.iterkeys():
>
>>>> d = dict(a=1)
>>>> keys = d.keys()
>>>> keys
> dict_keys(['a'])
>>>> for k in keys:
> ... d["b"] = 42
> ...
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> RuntimeError: dictionary changed size during iteration
>>>> keys
> dict_keys(['a', 'b'])
>
> You now have to create the list explicitly to avoid the error:
>
>>>> d = dict(a=1)
>>>> keys = list(d.keys())
>>>> for k in keys:
> ... d["b"] = 42
> ...
>>>> d
> {'a': 1, 'b': 42}
>>>> keys
> ['a']
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