dictionary size changed during iteration

[Laszlo Nagy]

Given this iterator:

class SomeIterableObject(object):
    ....
    ....
    def __iter__(self):
        ukeys = self.updates.keys()
        for key in ukeys:
            if self.updates.has_key(key):
                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?

Thanks,

   Laszlo

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