Is the goal to allow them to consume a finite generator of *unknown* length
(requires reservoir sampling
https://en.wikipedia.org/wiki/Reservoir_sampling with N random calls,
which seemed to be the rub before?) or just consume a generator with known
length that's not indexable (a rare beast?). Consuming iterables if they
have a length like below wouldn't be so bad, but might be too niche.
class X:
def __init__(self, ele): self.ele = ele
def __len__(self): return len(self.ele)
def __iter__(self): return iter(self.ele)
x = X([1, 2, 3, 4, 5])
random.choice(x) # TypeError: 'X' object does not support indexing
Would allowing an optional 'len' argument alongside the iterator to
sample/choice be too narrow to be useful?
On Wed, Nov 30, 2016 at 2:21 PM, Bernardo Sulzbach <
mafagafogiga...@gmail.com> wrote:
> On 2016-11-30 17:57, Chris Kaynor wrote:
>
>> On Wed, Nov 30, 2016 at 11:52 AM, Chris Kaynor <ckay...@zindagigames.com>
>> wrote:
>>
>>> There are also issues with how it should behave on iterables that
>>> cannot be re-iterated (eg, random.choice will consume the iterator,
>>> and could only be called once safely).
>>>
>>
>> I meant to include a sample in my previous e-mail:
>>
>> Consider that this code will not produce the "correct" results (for a
>> reasonable definition of correct):
>>
>> a = (i for i in range(100)) # Pretend this does something more
>> interesting, and isn't a trivial generator - maybe a file object
>> reading by line.
>> randomEntries = [random.choice(a) for i in range(10)]
>>
>
> In such a case you should explicitly use a sample.
>
> I see your example as the caller's fault, which ignored the fact that the
> iterator would change after calls to choice.
>
> Hold the first 10 (in this case). For every subsequent element, randomly
> choose to replace one of the "held" ones by it (with a diminishing
> probability).
>
> Assume this does not offer the same performance as loading everything into
> memory. But it isn't meant to do so, as if you need / can / want, you could
> just shove it all into a list and use what we currently have.
>
> --
> Bernardo Sulzbach
> http://www.mafagafogigante.org/
> mafagafogiga...@gmail.com
> _______________________________________________
> Python-ideas mailing list
> Python-ideas@python.org
> https://mail.python.org/mailman/listinfo/python-ideas
> Code of Conduct: http://python.org/psf/codeofconduct/
>
_______________________________________________
Python-ideas mailing list
Python-ideas@python.org
https://mail.python.org/mailman/listinfo/python-ideas
Code of Conduct: http://python.org/psf/codeofconduct/
