On May 22, 9:46 am, "J. Cliff Dyer" <j...@sdf.lonestar.org> wrote:
> You don't need a reset method. There is no hard and fast rule that
> __iter__ must return the object itself. It just needs to return an
> iterator.
I disagree.
If ITRATOR is a true iterator, ITRATOR.__iter__() must return
ITERATOR.
If ITERABLE is an iterable (but not necessarily an iterator)
ITRABLE.__iter__() must return an iterator.
> For example:
>
> >>> l = [1,2,3]
> >>> l.__iter__()
>
> <listiterator object at 0x7fd0da315850>>>> l is l.__iter__()
>
> False
[1,2,3] is an iterable but not an iterator, so this False result is
expected.
Compare this with the following.
>>> ii = iter([1,2,3]) # ii is an iterator.
>>> next(ii)
1
>>> jj = ii.__iter__() # call __iter__ method on an iterator
>>> ii is jj
True
>>> next(jj)
2
> Just create a class with an __iter__ method that returns a reset
> iterator object.
>
> class X(object):
> def __init__(self, max=3):
> self.counter = 0
> self.max = max
> def __iter__(self):
> return self
> def next(self):
> if self.counter < self.max:
> self.counter += 1
> return self.counter
> else:
> raise StopIteration
>
> class Y(object):
> def __iter__(self):
> return X()
>
> In this setup, X has the problem you are trying to avoid, but Y behaves
> as a resettable iterable.
> y = Y()
This does not work.
With this, y is not an interator, and not even an iterable.
> for c in y:
This produces an error because by definition of for-loops
it is executed the same way as:
temp_iterator = iter(y) # temp_iterator is y
while True:
try:
print(next(temp_iterator)) # temp_iterator does not support
__next__()
except StopIteration:
break
Jan
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