On Thu, Jul 23, 2020, at 05:14, Peter Slížik wrote: > > Works in what way? You can't use it in a 'for' loop if it doesn't > > define __iter__. > > > > class Iterable: > def __iter__(self): > return Iterator(...) > > class Iterator: > def __next__(self): > return <next item> > > # No __iter__ here. > # I've just forgotten to def it. > > With this setup, using for to iterate over Iterable *will* still work, > though you cannot use the trick described below.
Sure, but you can't use for to iterate over _Iterator itself_, or do anything else useful with it. >>> class Iterator: ... def __init__(self): self.done=False ... def __next__(self): ... if self.done: raise StopIteration ... self.done = True ... return 1 ... >>> [*Iterator()] >>> [*map(lambda x:x, Iterator())] >>> [*filter(lambda x:True, Iterator())] >>> for x in Iterator(): pass ... >>> [x for x in Iterator()] [all of the above have the exact same exception] Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'Iterator' object is not iterable >>> def gen(): ... yield from Iterator() ... >>> [*gen()] Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 2, in gen TypeError: 'Iterator' object is not iterable -- https://mail.python.org/mailman/listinfo/python-list
