Marko Rauhamaa wrote:
> Erik <pyt...@lucidity.plus.com>:
>
>> On 01/04/16 15:34, Marko Rauhamaa wrote:
>>> Chris Angelico <ros...@gmail.com>:
>>>
>>>> *A range object is not an iterator.*
>>>
>>> We now have learned as much.
>>>
>>> However, doesn't that extra level of indirection seem like an odd
>>> choice?
>>
>> [...]
>>
>> If you write your own class which has an __iter__ method, would you
>> [...] expect both iterators to be independent and both return the
>> 'foo', 'bar', 'baz' sequence (where that is the hypothetical result of
>> iterating over your object)?
>>
>> If you now replace MyClass() with range(10), why would you expect the
>> two iterators to be related?
>
> I simply had thought of range() returning an iterator. I would expect an
> iterator to behave like one.
>
> There's a bit of a cognitive dissonance between iterables and iterators.
> On the one hand, they behave identically in many contexts. On the other
> hand, the distinction is crucial in some special cases.
You're missing a key point. All (well-behaved) iterators are iterables,
with their __iter__ method returning themselves.
for x in y:
...
implies:
try:
_it = iter(y)
while True:
x = next(_it)
...
except StopIteration:
pass
That's true for any iterable y, including a y which is itself an
iterator. You still call iter() on it, and get _it, the iterator over
y, which if y is an iterator is the same thing as y.
--
Rob Gaddi, Highland Technology -- www.highlandtechnology.com
Email address domain is currently out of order. See above to fix.
--
https://mail.python.org/mailman/listinfo/python-list
