How to parametrise or make functions generic in Python?

Question

I am using a Python library (APScheduler) that requires some function handlers. All these handlers functions are almost the same. The only difference is a "constant" (as in, logic is the same; only the constant used to reference some data structures is different).

I would like to have a single generic function for all the handlers such that I can minimise my code or not having to add new functions when I add new types. Moreover, this enables me to have my types declared in a configuration file.

In Javascript this would be possible like this:

function staticFunction(args) {
    // ... this function I have to parameterise
};

function factory(type) {
    return function(args) {
        // ... this function is parametrised with "type"
    };
}

addHandler(staticFunction)
addHandler(factory("apples"));
addHandler(factory("oranges"));

How do I do the same in Python?

Martijn Pieters · Accepted Answer · 2018-10-16 16:06:07Z

4

You can do exactly the same thing in Python; you can create a nested function that'll have access to type as a closure:

def factory(type):
    def nested(args):
        # do something with `type`
    return nested

add_handler(factory('apples'))

There are more ways you can bind a parameter to a callable; you could use a lambda to proxy the function call:

def static_function(type, args):
    # ...

add_handler(lambda args: static_function('apples', args))

or you could use a functools.partial() object to bind arguments to a callable:

from functools import partial

add_handler(partial(static_function, 'apples'))

answered Oct 16, 2018 at 16:06

Martijn Pieters

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