On Tue, Sep 14, 2021 at 9:31 PM Steven D'Aprano <st...@pearwood.info> wrote:
> If it helps, I have tons of code that tests for iterators using: > > iter(obj) is obj > > That has been a documented requirement for the iterator protocol > forever. Its in the PEP. > > "A class that wants to be an iterator should implement two methods: a > next() method that behaves as described above, and an __iter__() method > that returns self." > > https://www.python.org/dev/peps/pep-0234/ > However, the description clarifies that the reason for requiring __iter__ is weaker than the reason for requiring __next__. > We have objects such that: > > iter(obj) > > returns an iterator, but aren't themselves iterators. Yeah, those are Iterables. > The most common > example of that would be, I think, classes that define __iter__ as a > generator method: > > class A: > def __iter__(self): > for x in range(10): > yield x > > Then we have actual iterators, like iter(A()). They define `__iter__` > that returns self. > > I don't know what I would call an object that only has __next__, > apart from "broken" :-( > It's still an iterator, since it duck-types in most cases where an iterator is required (notably "for", which is the primary use case for the iteration protocols -- it's in the first sentence of PEP 234's abstract). -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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