How to overwrite class method in python?

Question

I'm trying to change the method of class on the fly. I can change it using the class name, like here:

class Foo:
    def __init__(self, x):
        self.x = x

    def method(self):
        print("original method")
        return self.x


def new_method(self):
     print("new method")
     return self.x

Foo.method = new_method
foo = Foo(1)
print(foo.method())  # Works fine

But I'd like to change the method using the object name, not the class, and it raises an error:

foo = Foo(1)
foo.method = new_method
print(foo.method())  # TypeError: new_method() missing 1 required positional argument: 'self'

Would appreciate any help on this matter

Samwise · Accepted Answer · 2022-09-30 14:40:47Z

6

You need to provide the binding for self. This is done automatically for you when a method is defined in a class, but not when you monkey-patch an object.

>>> foo = Foo(1)
>>> foo.method = lambda: new_method(foo)
>>> print(foo.method())
new method
1

answered Sep 30, 2022 at 14:40

Samwise

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