[Python-3000] Fwd: Re: PEP: rename it.next() to it.__next__(), add a next() built-in

[Raymond Hettinger]

[Raymond]
>> My thought here is that iterators should always be a separate object -- there is no good reason for dir(iter(myfile)) to expose methods that have nothing to do with iteration.  In the case of files, it would not be hard to have a singleton file-iterator object.

[GvR]
>The question isn't how hard it would be, but whether it would be the
>right thing to do. For iterators where (by nature of the object being
>iterated over) there's only one iterator possible, I think returning
>self is the right thing to do, as it makes it abundantly clear that
>multiple parallel iterations are unsupported.

I don't follow how returning self makes anything clear -- the only way to know that self was returned is to check object ids or to guess why dir() on the iterator returns all of the file methods:


>>> f = open('tmp.txt')
>>> it1 = iter(f)
>>> it2 = iter(f)
>>> map(id, [f, it1, it2])    # only this check shows that 'iter(f) is f'
[3083536096L, 3083536096L, 3083536096L]
>>> dir(it1)
['__class__', '__delattr__', '__doc__', '__enter__', '__exit__', '__getattribute__', '__hash__', '__init__', '__iter__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__', 'close', 'closed', 'encoding', 'fileno', 'flush', 'isatty', 'mode', 'name', 'newlines', 'next', 'read', 'readinto', 'readline', 'readlines', 'seek', 'softspace', 'tell', 'truncate', 'write', 'writelines', 'xreadlines']

ISTM, we might as well make the singletonness explicit and hide the file methods from the iterator object (nothing good can come from conflating file ops with iteration).


Raymond