[Python-Dev] Possible patch for functools partial - Interested?

[Steve Holden]

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.

> 
> [...]
>> Similarly, if you wanted p1==p2, why not write
>>
>>     p1 = partial(operator.add)
>>     p2 = p1
> 
> I thought the OP gave a use-case. He's generating "jobs" (partial 
> applied to a callable and arguments), and wanted to avoid duplicated 
> jobs.
> 
> 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?

regards
 Steve

> +0.5 on comparing equal.
> +1 on a nicer repr for partial objects.
> 
> 
> 


-- 
Steve Holden           +1 571 484 6266   +1 800 494 3119
See PyCon Talks from Atlanta 2010  http://pycon.blip.tv/
Holden Web LLC                 http://www.holdenweb.com/
UPCOMING EVENTS:        http://holdenweb.eventbrite.com/