[Python-ideas] Introduce collections.Reiterable

[Neil Girdhar]

Sorry, never mind, the documentation is clear.  I got caught up with
collections.abc page and didn't click through.   At least I have Antoine's
code now to use in my project whether it gets added to the standard library
or not :)

Best,

Neil


On Thu, Sep 19, 2013 at 5:38 AM, Neil Girdhar <mistersheik at gmail.com> wrote:

> First of all, that's amazing and exactly what I was looking for.
>
> Second, sorry Nick, I guess we were talking past each other and I didn't
> understand what you were getting at.  From the collections.abc
> documentation, I imagined that subclasses are more restricted and therefore
> can do more than their superclasses.  However, as you were trying to tell
> me things that are "Iterators" (and thus also Iterable) can do *less* than
> things that are merely Iterable.  The former cannot be iterated over twice.
>   If I'm understanding this correctly, would it be nice if the
> documentation then made this promise (as I don't believe it does)?
>
> Best,
>
> Neil
>
>
> On Thu, Sep 19, 2013 at 5:30 AM, Antoine Pitrou <solipsis at pitrou.net>wrote:
>
>> Le Thu, 19 Sep 2013 04:59:35 -0400,
>> Neil Girdhar <mistersheik at gmail.com> a
>> écrit :
>> > Well, generators are iterable, but if you write a function like:
>> >
>> > def f(s):
>> >      for x in s:
>> >              do_something(x)
>> >      for x in s:
>> >              do_something_else(x)
>> >
>> > x should not be a generator.  I am proposing adding a function to
>> > itertools like auto_reiterable that would take s and give you an
>> > reiterable in the most efficient way possible.
>>
>> Try the following:
>>
>>
>> import collections
>> import itertools
>>
>>
>> class Reiterable:
>>
>>     def __init__(self, it):
>>         self.need_cloning = isinstance(it, collections.Iterator)
>>         assert self.need_cloning or isinstance(it, collections.Iterable)
>>         self.master = it
>>
>>     def __iter__(self):
>>         if self.need_cloning:
>>             self.master, it = itertools.tee(self.master)
>>             return it
>>         else:
>>             return iter(self.master)
>>
>> def gen():
>>     yield from "ghi"
>>
>> for arg in ("abc", iter("def"), gen()):
>>     it = Reiterable(arg)
>>     print(list(it))
>>     print(list(it))
>>     print(list(it))
>>
>>
>> I don't know if that would be useful as part of the stdlib.
>>
>> Regards
>>
>> Antoine.
>>
>>
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