What makes an iterator an iterator?

[Steven D'Aprano]

I thought that an iterator was any object that follows the iterator
protocol, that is, it has a next() method and an __iter__() method.

But I'm having problems writing a class that acts as an iterator. I have:

class Parrot(object):
    def __iter__(self):
        return self
    def __init__(self):
        self.next = self._next()
    def _next(self):
        for word in "Norwegian Blue's have beautiful plumage!".split():
            yield word

But this is what I get:

>>> P = Parrot()
>>> for word in P:
...     print word
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: iter() returned non-iterator of type 'Parrot'

Why is my instance not an iterator?

But I can do this:

>>> for word in P.next:
...     print word
...
Norwegian
Blue's
have
beautiful
plumage!

I find myself perplexed as to this behaviour.


-- 
Steven D'Aprano