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Re: Is there a canonical way to check whether an iterable is ordered?

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On Fri, Sep 19, 2014 at 8:59 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> Here's a proof of concept of what would be allowed:
>
> import random
> class MyDict:
>     def __init__(self, items):
>         self._items = list(dict(items).items())
>         self._flags = [False, False, False]
>     def keys(self):
>         k = [item[0] for item in self._items]
>         self._check(0)
>         return k
>     def values(self):
>         k = [item[1] for item in self._items]
>         self._check(1)
>         return k
>     def items(self):
>         k = self._items[:]
>         self._check(2)
>         return k
>     def _check(self, i):
>         self._flags[i] = True
>         if self._flags == [True, True, True]:
>             random.shuffle(self._items)
>             self._flags = [False, False, False]

Also, this can't possibly offer the same guarantee. Watch:

d = MyDict(some_lot_of_items)
d.values(); d.items()
# mutate the dict in whatever way you like
pairs = zip(d.keys(), d.values())

This might well create mismatched pairs, because after generating the
keys() return value, the list gets shuffled, prior to generating
values() in the same expression. This would not be allowed.

ChrisA

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Thread

Is there a canonical way to check whether an iterable is ordered? cool-RR <ram.rachum@gmail.com> - 2014-09-18 04:55 -0700
  Re: Is there a canonical way to check whether an iterable is ordered? Chris Angelico <rosuav@gmail.com> - 2014-09-18 22:10 +1000
    Re: Is there a canonical way to check whether an iterable is ordered? Roy Smith <roy@panix.com> - 2014-09-18 08:58 -0400
      Re: Is there a canonical way to check whether an iterable is ordered? Chris Angelico <rosuav@gmail.com> - 2014-09-18 23:33 +1000
        Re: Is there a canonical way to check whether an iterable is ordered? Roy Smith <roy@panix.com> - 2014-09-18 19:52 -0400
          Re: Is there a canonical way to check whether an iterable is ordered? Chris Angelico <rosuav@gmail.com> - 2014-09-19 12:45 +1000
          Re: Is there a canonical way to check whether an iterable is ordered? Terry Reedy <tjreedy@udel.edu> - 2014-09-19 18:02 -0400
          Re: Is there a canonical way to check whether an iterable is ordered? Chris Angelico <rosuav@gmail.com> - 2014-09-20 15:01 +1000
      Re: Is there a canonical way to check whether an iterable is ordered? Terry Reedy <tjreedy@udel.edu> - 2014-09-18 09:46 -0400
      Re: Is there a canonical way to check whether an iterable is ordered? Tim Chase <python.list@tim.thechases.com> - 2014-09-18 09:32 -0500
      Re: Is there a canonical way to check whether an iterable is ordered? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-09-19 15:15 +1000
        Re: Is there a canonical way to check whether an iterable is ordered? Chris Angelico <rosuav@gmail.com> - 2014-09-19 15:40 +1000
          Re: Is there a canonical way to check whether an iterable is ordered? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-09-19 20:59 +1000
            Re: Is there a canonical way to check whether an iterable is ordered? Chris Angelico <rosuav@gmail.com> - 2014-09-19 21:19 +1000
              Re: Is there a canonical way to check whether an iterable is ordered? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-09-19 21:58 +1000
                Re: Is there a canonical way to check whether an iterable is ordered? Chris Angelico <rosuav@gmail.com> - 2014-09-19 22:06 +1000
            Re: Is there a canonical way to check whether an iterable is ordered? Chris Angelico <rosuav@gmail.com> - 2014-09-19 21:25 +1000
              Re: Is there a canonical way to check whether an iterable is ordered? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-09-19 21:46 +1000
                Re: Is there a canonical way to check whether an iterable is ordered? Chris Angelico <rosuav@gmail.com> - 2014-09-19 21:56 +1000
                Re: Is there a canonical way to check whether an iterable is ordered? alister <alister.nospam.ware@ntlworld.com> - 2014-09-19 12:26 +0000
                Re: Is there a canonical way to check whether an iterable is ordered? Chris Angelico <rosuav@gmail.com> - 2014-09-19 22:36 +1000
  Re: Is there a canonical way to check whether an iterable is ordered? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-09-19 15:04 +1000

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