Python bind method to another instance

Question

I need to merge two methods from different instances of different classes to a single instance of a class.

For example I define two classes:

class A:
    def __init__(self):
        self.name = "a"

    def print_name(self):
        print(self.name)


class B:
    def __init__(self):
        self.name = "b"

    def print_name(self):
        print(self.name)

and then I will try to make another object c and its print_name method must return the results of a.print_name() and b.print_name() so I tried the following :

a = A()
b = B()
c = A()

c.name = "c"
c.print_name_1 = a.print_name
c.print_name_2 = b.print_name
def final_print(self):
    self.print_name_1()
    self.print_name_2()
c.print_name = MethodType(final_print, c)
c.print_name()

Expected output:

c
c

but I get :

a
b

I tried to use types.MethodType as described here but it creates some kind of a method which takes two arguments : the first one will be the 'a' instance and the second one will be the 'c' instance.

Any help to do that properly?

Overriding methods on a per-instance basis defeats the purpose of having a class, which is to provide a uniform interface for all instances of the class. — chepner
– chepner, Commented Sep 4, 2020 at 18:24
My goal is to create a new object by merging two others, I don't know how to do that with another way — Breeky
– Breeky, Commented Sep 4, 2020 at 18:26
Should c be an instance of A, or should it really be an instance of a new class? Also, do A and B really need to be separate classes, or can a and b be instances of the same class, just with different values for the name attribute? — chepner
– chepner, Commented Sep 4, 2020 at 18:29
So a,b,c inherit from the same class, let's call it Parent, but they are different classes with different methods — Breeky
– Breeky, Commented Sep 4, 2020 at 20:39

Breeky · Accepted Answer · 2020-09-06 17:17:04Z

1

I managed to succeed with this, thanks to this answer. I am using the __func__ attribute of a method. So here is the code :

c.name = "c"
c.print_name_1 = MethodType(lambda instance: copy.deepcopy(a.print_name).__func__(instance), c)
c.print_name_2 = MethodType(lambda instance: copy.deepcopy(b.print_name).__func__(instance), c)
def final_print(self):
    self.print_name_1()
    self.print_name_2()
c.print_name = MethodType(final_print, c)
c.print_name()

answered Sep 6, 2020 at 17:17

Breeky

618 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

tripleee Over a year ago

While this works, it's probably not the correct solution to whatever end goal you are hoping to achieve.

Breeky Over a year ago

To describe more precisely my intend, it is to create a parent class Parent, and two types of parent called A and B which have their own implementation of the function print_name. Here I want to merge A and B to create a new class or instance dynamically (in the code above it is c) that has a function with the same name (i.e. print_name), and this function must execute first the method print_name defined in A, and then the method print_name defined in B. But the self argument in these functions refers to the instance c. So do you have any idea how to merge this methods into one dynamically ?

tripleee Over a year ago

That's still crazy. Why do you want to do that? Having methods with different names in A and B would let you easily have a wrapper which dispatches the method with a different name, so in A you would have def method(): return(a_method) and in B def method: return(b_method). Now in C you can easily inherit from both A and B and def method: a_method(); return b_method() or whatever.

tripleee Over a year ago

Tangentially, maybe see also mixins.

tripleee Over a year ago

Yes yes, so define it like A: def print_name(): return a_specific_print_name() and B: def print_name(): return b_specific_print_name() and then in C def print_name(): a_specific_print_name(); b_specific_print_name()

|

Collectives™ on Stack Overflow

Python bind method to another instance

1 Answer 1

6 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related