[Python-ideas] Make partial a built-in

[Dan Sommers]

On Tue, 20 Sep 2016 15:29:36 +0000, אלעזר wrote:

> The alternative to partial is writing a closure in the form of a
> function, that needs to be carefully inspected to verify that it is
> indeed just a partial application and not something more complex. It
> has more opportunity for introducing an error. And it's longer and
> adds distance between related parts of the code.

While I'm not usually one to promote object oriented programming,
another Python alternative is a class with a __call__ method; e.g.:

    class Adder:
        def __init__(self, addend_one):
            self.addend_one = addend_one
        def __call__(self, addend_two):
            return self.addend_one + addend_two

    add_5 = Adder(5)
    print(add_5(4))

I like the way the whole thing is bundled up into a class.  Yes, it's
more verbose than a lambda expression or a partial function application,
but I find it very readable and its intent is usually pretty obvious.

Instances are closures in disguise (and they're all just different ways
of hiding state of one kind or another).