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

[Andrew Barnert]

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.

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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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> -- 
> Keeping medicines from the bloodstreams of the sick; food 
> from the bellies of the hungry; books from the hands of the 
> uneducated; technology from the underdeveloped; and putting 
> advocates of freedom in prisons.  Intellectual property is
> to the 21st century what the slave trade was to the 16th.
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