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 <mafagafogigante@gmail.com> wrote:
On 2016-11-30 17:57, Chris Kaynor wrote:
On Wed, Nov 30, 2016 at 11:52 AM, Chris Kaynor <ckaynor@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/
mafagafogigante@gmail.com
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