Pass a method to a function before object instantiation in python

Question

I have a class called "App" which has several methods. I want to write a function which creates several instances of App and use one of those methods for each instance. How can I pass the method name as argument to the function ?

Code example:

class App(object):

    def __init__(self, id):
        self.id = id

    def method_1(self):
        result1 = self.id + 1
        return result1

    def method_2(self):
        result2 = self.id + 2
        return result2

def use_method_for_each_instance(method):
    all_results = []
    for id in id_list:
        app_instance = App(id)
        all_results.append(app_instance.method())
    return all_results

id_list = [1,2,3]
use_method_for_each_instance(method_1)

With this code I get "NameError: name 'method_1' is not defined", which is logical since method_1 is only defined when an "App" object is created. Can you help me to change my code in order to avoid that error?

Answer 1

You can use function from class namespace.

def use_method_for_each_instance(method):
    all_results = []
    for id in id_list:
        app_instance = App(id)
        all_results.append( method(app_instance) )
    return all_results

id_list = [1,2,3]
use_method_for_each_instance(App.method_1)

Answer 2

You can pass the name of the method as a string and then you can use getattr to retrieve the method from your app_instance.

Like so:

def use_method_for_each_instance(method):
    for id in id_list:
        app_instance = App(id)
        method_to_call = getattr(app_instance, method)
        #                   ^ gets callable method from instance
        all_results.append(method_to_call())
    return all_results

use_method_for_each_instance("method_1")