Why does a Python Iterator need an iter method that simply returns self?

Question

I understand that the standard says that it does but I am trying to find the underlying reason for this.

If it simply always returns self what is the ne

Answer 1

for loops should work with iterables, so for i in something: automatically calls iter(something) to get an iterator and iterates over said iterator. Now if iterators weren't iterable too (i.e. did not define __iter__), you couldn't use for loops with iterators, i.e.:

items = [1, 2, 3]
# this would work
for item in items: pass
# this wouldn't
it = iter(items)
for item in it: pass

Therefore, iterators should be iterables too. The alternative, "somehow detecting" iterators and not calling iter on them, is hacky and fragile (how would you decide that?).