[Python-ideas] An ABC representing "Iterable, Sized, Container"

[Nick Coghlan]

On 22 July 2016 at 10:29, Guido van Rossum <guido at python.org> wrote:
> On Thu, Jul 21, 2016 at 5:05 PM, Thomas Nyberg <tomuxiong at gmail.com> wrote:
>> On 07/21/2016 07:58 PM, Guido van Rossum wrote:
>>>
>>> But there's already Container which means "supports __contains__".
>>>
>>> Collection might cause confusing with the module name collections.
>>>
>>> Otherwise either would be a good candidate...

As far as the original "Sized Iterable Container" question goes, would
FiniteContainer work?

- it's countable/iterable
- it has a quantifiable size
- you can do membership tests on it

Countable & quantifiable = finite, membership testing = container,
hence FiniteContainer

>> Coming out of lurking...
>>
>> StaticIterable? ConstIterable? Something to indicate that if you just
>> iterate over it you keep getting the same thing?
>
> Neither "static" nor "const" convey the right meaning.
>
>> Personally I think Reiterable is about as clear as it ever will be...
>
> Yeah, I think that's my conclusion as well.

With the semantics being "iter(x) is not x"?

That seems reasonable to me, as I spent some time think about whether
or not this is a distinct idea from the "Sized Iterable Container"
question, and it's pretty easy to demonstrate that it is:

    >>> class ReiterableCounter:
    ...     def __iter__(self):
    ...         x = 0
    ...         while True:
    ...             yield x
    ...             x += 1
    ...
    >>> ctr = ReiterableCounter()
    >>> for x in ctr:
    ...     print(x)
    ...     if x > 1: break
    ...
    0
    1
    2
    >>> for x in ctr:
    ...     print(x)
    ...     if x > 1: break
    ...
    0
    1
    2

(The same example works by returning any non-terminating iterator from __iter__)

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia