[Python-ideas] Fwd: Extremely weird itertools.permutations

[Jonathan Brandvein]

I think it's fair to use {3.0, 3} as precedent. But note that transitivity
is not required by the __eq__() method. In cases of intransitive equality
(A == B == C but not A == C), I imagine the result should be ill-defined in
the same way that sorting is when the key function is inconsistent.

Jon


On Fri, Oct 11, 2013 at 4:19 PM, Andrew Barnert <abarnert at yahoo.com> wrote:

> I think equality is perfectly reasonable here. The fact that {3.0, 3} only
> has one member seems like the obvious precedent to follow here.
>
> Sent from a random iPhone
>
> On Oct 11, 2013, at 13:02, David Mertz <mertz at gnosis.cx> wrote:
>
> What would you like this hypothetical function to output here:
>
> >>> from itertools import permutations
> >>> from decimal import Decimal as D
> >>> from fractions import Fraction as F
> >>> items = (3, 3.0, D(3), F(3,1), "aa", "AA".lower(), "a"+"a")
> >>> list(permutations(items))
>
> It's neither QUITE equality nor identity you are looking for, I think, in
> nonredundant_permutation():
>
> >> "aa" == "AA".lower(), "aa" is "AA".lower()
> (True, False)
> >>> "aa" == "a"+"a", "aa" is "a"+"a"
> (True, True)
> >>> D(3) == 3.0, D(3) is 3.0
> (True, False)
>
> On Fri, Oct 11, 2013 at 11:38 AM, Neil Girdhar <mistersheik at gmail.com>wrote:
>
>> "It is universally agreed that a list of n distinct symbols has n!
>> permutations. However, when the symbols are not distinct, the most common
>> convention, in mathematics and elsewhere, seems to be to count only
>> distinct permutations." —
>> http://stackoverflow.com/questions/6534430/why-does-pythons-itertools-permutations-contain-duplicates-when-the-original
>> .
>>
>>
>> Should we consider fixing itertools.permutations and to output only
>> unique permutations (if possible, although I realize that would break
>> code). It is completely non-obvious to have permutations returning
>> duplicates. For a non-breaking compromise what about adding a flag?
>>
>> Best,
>> Neil
>>
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>
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> to the 21st century what the slave trade was to the 16th.
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