In article <[email protected]>,
Terry Reedy <[email protected]> wrote:
>
>Changing a list while iterating through it is possible, sometimes
>useful, but error prone, especially with insert or delete. Changing a
>dict while iterating through it is prohibited since the iteration order
>depends on the exact internal structure. That in turn depends on the
>history of additions and deletions.
Although I agree in general with your warning, you are factually
incorrect about dicts:
>>> d = {1:2, 3:4}
>>> i = iter(d)
>>> i.next()
1
>>> d[1] = 'foo'
>>> d
{1: 'foo', 3: 4}
Essentially, the prohibition is against changing the *keys* of lists and
dicts (where list keys are the indexes). So what you can't do is add or
delete dict keys and changing the position or order of list elements is
a Bad Idea. But changing dict or list values is fine as long as you're
careful that's *all* you're doing. Python newcomers are best off simply
avoiding any list/dict mutation during iteration.
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