Re: reversed(zip(...)) not working as intended

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From	Tim Chase <python.list@tim.thechases.com>
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Subject	Re: reversed(zip(...)) not working as intended
Date	Sun, 6 Mar 2016 12:51:53 -0600
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On 2016-03-06 12:38, Tim Chase wrote:
> On 2016-03-06 19:29, Sven R. Kunze wrote:
> > what's the reason that reversed(zip(...)) raises as a TypeError?
> 
> I'm not sure why reversed() doesn't think that the thing returned by
> zip() isn't a sequence.

Ah, a little more digging suggests that in 2.x, zip() returned a list
which "has a __reversed__() method [and] supports the sequence
protocol (the __len__() method and the __getitem__() method with
integer arguments starting at 0)."

In 3.x, zip() returns a generic iterator which neither has a
__reversed__() method nor has __len__() and __getitem__() methods.

So it looks like one needs to either

   results = reversed(list(zip(...)))

or, more efficiently (doing it with one less duplication of the list)

   results = list(zip(...))
   results.reverse()

-tkc

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Re: reversed(zip(...)) not working as intended Tim Chase <python.list@tim.thechases.com> - 2016-03-06 12:51 -0600

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