[Python-ideas] Introduce collections.Reiterable

[Tim Delaney]

On 20 September 2013 21:10, Steven D'Aprano <steve at pearwood.info> wrote:

>
> py> class Seq:
> ...     def __getitem__(self, index):
> ...             if 0 <= index < 5: return index+1000
> ...             raise IndexError
> ...
> py> s = Seq()
> py> isinstance(s, Iterable)  # The ABC claims Seq is not iterable.
> False
> py> for x in s:  # But it actually is.
> ...     print(x)
> ...
> 1000
> 1001
> 1002
> 1003
> 1004
>
>
> Can anyone convince me this is not a bug in the Iterable ABC?
>

I think there is a distinction here between collections.Iterable (as a
defined ABC) and something that is "iterable" (lowercase "i"). As you've
noted, an "iterable" is "An object capable of returning its members one at
a time".

So I think a valid definition of reiterable (barring pathological cases) is:

    obj is not iter(obj)

(assuming of course that obj is iterable).

Python 3.3.0 (v3.3.0:bd8afb90ebf2, Sep 29 2012, 10:57:17) [MSC v.1600 64
bit (AM
D64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> class Seq:
...     def __getitem__(self, index):
...         if 0 <= index < 5:
...             return index+1000
...         raise IndexError
...
>>> s = Seq()
>>> s is iter(s)
False
>>> i = iter(s)
>>> i is iter(i)
True
>>> t = ()
>>> t is iter(t)
False
>>> i = iter(t)
>>> i is iter(i)
True
>>>

Tim Delaney
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