Use-cases for alternative iterator

[Steven D'Aprano]

The iter() built-in takes two different forms, the familiar 
iter(iterable) we all know and love, and an alternative form:

iter(callable, sentinel)

E.g.:

>>> T = -1
>>> def func():
...     global T
...     T += 1
...     return T
...
>>> it = iter(func, 3)
>>> next(it)
0
>>> next(it)
1
>>> next(it)
2
>>> next(it)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration



I've never seen this second form in actual code. Does anyone use it, and 
if so, what use-cases do you have?



-- 
Steven
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