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Fri May 7 21:13:50 CEST 2010 · https://mail.python.org/pipermail/python-dev/2010-May/099993.html

On Sat, 8 May 2010 03:57:06 am Steve Holden wrote:
> Steven D'Aprano wrote:
> > On Sat, 8 May 2010 02:07:55 am Rob Cliffe wrote:
> >> Sorry to grouse, but isn't this maybe being a bit too clever?
> >> Using your example,
> >>     p1 = partial(operator.add)
> >> is creating a callable, p1, i.e. a sort of function.  Yes I know
> >> technically it's not a function, but it behaves very much like
> >> one.
> >>
> >> Now, if I write
> >>
> >>     def f1(x,y): return x+y
> >>     def f2(x,y): return x+y
> >>
> >> I don't expect  f1==f2 to be True, even though f1 and f2 behave in
> >> exactly the same way,
> >> and indeed it is not.
> >
> > I do expect f1==f2, and I'm (mildly) disappointed that they're not.
>
> How about
>
> def f1(x, y): return x+y
> def f2(x, y): return y+x
>
> As you know, there are limits to everything. It seems to me that
> while pure mathematics can (sometime) easily determine functional
> equivalence, once you get to code it's a lot harder because there are
> semantic constraints that don't apply in pure mathematics.

This being Python, we can't assume x+y is always equal to y+x, so in 
your example I wouldn't expect them to be equal. And thus I avoid your 
trap :)

What you say is correct in general. I understand the arguments against 
making function equality more sophisticated than just identity testing: 
there aren't many use-cases for it, and it is potentially a lot of work 
depending on how clever you try to be. But if it came for free, it 
would be a sweet trick to impress your friends and scare your enemies.

[...]
> > I think it is reasonable to expect that partial(operator.add, 2)
> > compares equal to partial(operator.add, 2). I don't think he's
> > suggesting it should compare equal to partial(lambda x,y: x+y, 2).
>
> Which absence, presumably, also mildly disappoints you?

Only in the sense that in a perfect world where language features had 
benefits but no costs, I would expect nothing less.

-- 
Steven D'Aprano

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[Python-Dev] Possible patch for functools partial