[Python-Dev] Possible patch for functools partial (original) (raw)

Rob Cliffe rob.cliffe at btinternet.com
Fri May 7 18:07:55 CEST 2010

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. If I wanted it to be true, I should have written

def f1(x): return x+y
f2=f1

I find this behaviour natural and expected, both in my example and yours (although maybe I've just got used to Python's behaviour).

Similarly, if you wanted p1==p2, why not write

p1 = partial(operator.add)
p2 = p1

Maybe I could be persuaded otherwise by a convincing use case, but I rather doubt it. Rob Cliffe

----- Original Message ----- From: "VanL" <van.lindberg at gmail.com> To: <python-dev at python.org> Sent: Friday, May 07, 2010 3:37 PM Subject: [Python-Dev] Possible patch for functools partial - Interested?

Howdy all -

I have an app where I am using functools.partial to bundle up jobs to do, where a job is defined as a callable + args. In one case, I wanted to keep track of whether I had previously seen a job, so I started putting them into a set... only to find out that partials never test equal to each other:

import operator from functools import partial p1 = partial(operator.add) p2 = partial(operator.add) p1 == p2 False seen = set();seen.add(p1) p2 in seen False I created a subclass of functools.partial that provides appropriate eq and hash methods, so that this works as expected. I called the subclass a Job: j1 = Job(operator.add) j2 = Job(operator.add) j1 == j2 True seen = set();seen.add(j1) j2 in seen True j1 is j2 False While I was at it, I also added a nice repr. Would this group be interested in a patch, or is this not interesting? Thanks, Van

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