Python：在运行时更改方法和属性

Question

我想在Python里创建一个类，这个类可以随时添加和删除属性和方法。我该怎么做呢？

哦，对了，请不要问我为什么要这样做。

Answer 1

>>> f = types.MethodType(talk, puppy, Dog)
>>> puppy.talk = f # add method to specific instance

一个可能有趣的替代方案是使用 types.MethodType，可以利用函数是描述符这一事实：

>>> puppy.talk = talk.__get__(puppy, Dog)

Answer 2

这个例子展示了在一个类和一个实例上添加方法的区别。

>>> class Dog():
...     def __init__(self, name):
...             self.name = name
...
>>> skip = Dog('Skip')
>>> spot = Dog('Spot')
>>> def talk(self):
...     print 'Hi, my name is ' + self.name
...
>>> Dog.talk = talk # add method to class
>>> skip.talk()
Hi, my name is Skip
>>> spot.talk()
Hi, my name is Spot
>>> del Dog.talk # remove method from class
>>> skip.talk() # won't work anymore
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: Dog instance has no attribute 'talk'
>>> import types
>>> f = types.MethodType(talk, skip, Dog)
>>> skip.talk = f # add method to specific instance
>>> skip.talk()
Hi, my name is Skip
>>> spot.talk() # won't work, since we only modified skip
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: Dog instance has no attribute 'talk'

Answer 3

我想在Python中创建一个类，这个类可以让我添加和删除属性和方法。

import types

class SpecialClass(object):
    @classmethod
    def removeVariable(cls, name):
        return delattr(cls, name)

    @classmethod
    def addMethod(cls, func):
        return setattr(cls, func.__name__, types.MethodType(func, cls))

def hello(self, n):
    print n

instance = SpecialClass()
SpecialClass.addMethod(hello)

>>> SpecialClass.hello(5)
5

>>> instance.hello(6)
6

>>> SpecialClass.removeVariable("hello")

>>> instance.hello(7)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'SpecialClass' object has no attribute 'hello'

>>> SpecialClass.hello(8)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: type object 'SpecialClass' has no attribute 'hello'