How to assign class method to class attribute?

This question already has an answer here:

Calling a function of a module by using its name (a string) 10 answers

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Note that when you try:

class A:
    MAP = {
        'add' : A.add(x, y),
        'subtract' : A.subtract(x, y),
    }

you are trying to access eg A.add before the name A exists (the class isn't bound to the name until definition completes) and before the name add exists (you haven't defined that method yet). Everything at the top level of the class definition is done in order .

---

You need to put the class methods into the dictionary after the class has been defined (they don't become callable until definition is complete):

class A:

    MAP = {}

    @classmethod
    def add(cls, x, y):  # note colon
        return x + y

    @classmethod
    def subtract(cls, x, y):  # also here
        return x - y

A.MAP['add'] = A.add
A.MAP['subtract'] = A.subtract

Note that, as neither class method uses cls , you could make them @staticmethod s instead. Or just use functions - Python isn't Java, you don't need to put everything into a class.

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Alternatively, you can use getattr to access attributes (including class methods) by name:

>>> class A:

        @classmethod
        def add(cls, x, y):
            return x + y

        @classmethod
        def subtract(cls, x, y):
            return x - y


>>> getattr(A, 'add')(1, 2)
3

---

请不要使用python编程，而应使用更标准的oop方法，例如：

#!/usr/bin/env python

class A:

    def __init__(self):
        pass

    @classmethod
    def add(self, x, y):
        return x + y

    @classmethod
    def subtract(self, x, y):
        return x - y

if __name__ == "__main__":
    a = A()
    print a.add(1,2)  # ans: 3
    print a.subtract(2,1) # ans: 1

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