Python: Assigning class method to a variable-CodePudding

I have a number of methods in a class and I need to call a specific one. I tried something like this, but got an AttributeError

class MyClass:
    def first(a, b):
        return a   b
    def second(a, b):
        return a * b

a = 2
b = 3

first_func = MyClass.first
second_func = MyClass.second

my_obj = MyClass()

I expect something of a following to work, but I'm getting this exception:

my_obj.first_func(a, b)   my_obj.second_func(a, b) == 11

So is there a way to do it?

CodePudding user response：

Since your methods do not have self parameters, they are "static" and do not depend on the intantiated object. You can call your functions this way:

first_func(a, b)  # no my_obj

If in reality they do depend on the object, you would write:

class MyClass:
    def first(self, a, b):
        return a   b
    def second(self, a, b):
        return a * b

And they you can call the method "on" an object:

my_obj = MyClass()
my_obj.first(a, b)

Or, with your initial notation:

first_func = MyClass.first
first_func(my_obj, a, b)

(same for your second method)

CodePudding user response：

Function definition in a class should contain 'self' as a param

class MyClass:
    def first(self,a, b):
        return a   b
    def second(self,a, b):
        return a * b

a = 2
b = 3

first_func = MyClass.first
second_func = MyClass.second

my_obj = MyClass()
first_func(my_obj,a, b)   second_func(my_obj,a, b) == 11