Alan McIntyre wrote:
I think it's because you're modifying the list as you're iterating over it.
One last clarification on this. It's OK to modify the elements of a list, but not the list itself while iterating over it... is that the correct way to think about this?
Correct - the iteration code bases the iteration on the *old* list structure, so you can end up with odd behaviour.
Py> l = range(10) Py> for i in l: del l[i] ... Traceback (most recent call last): File "<stdin>", line 1, in ? IndexError: list assignment index out of range Py> l [1, 2, 4, 5, 7, 9]
Dictionaries have the same problem, but they include some guards that try to detect it:
Py> d = dict.fromkeys(range(10)) Py> for i in d: del d[i] ... Traceback (most recent call last): File "<stdin>", line 1, in ? RuntimeError: dictionary changed size during iteration
This feature can't be added to lists because it is possible to iterate sensibly over a mutating list:
Py> l = range(10) Py> for i in reversed(l): del l[i] ... Py> l []
Cheers, Nick.
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Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia
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