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'] -- http://mail.python.org/mailman/listinfo/python-list