使用 class 方法作为 function 的参数

Question

I want to pass an class method as an argument to a function which applies the method to an instance. I wrote a simplified example of my problem down, which does not work. Is there a way to do this in python?

class A:
    def __init__(self):
        self.values = [1,2,3]
        
    def combine(self) -> int:
        return sum(self.values)
    
    def return_zero(self) -> int:
        return 0
    

def apply_func(instance, func):
    return instance.func()


print(apply_func(A(), A.combine))

> AttributeError: 'A' object has no attribute 'func'
        

Answer 1

You could use getattr() :

def apply_func(instance, func):
    fn = getattr(instance, func)
    return fn()


print(apply_func(A(), 'combine'))

Out:

6

Answer 2

Instead of

def apply_func(instance, func):
    return instance.func()

you should do:

def apply_func(instance, func):
    return func(instance)

Remember the method is defined as def combine(self) - by calling func(instance) , the instance simply becomes that self .

Try it online!