动态地使用装饰器从类外部添加方法

Question

Two things I'm having trouble with. Adding a method from outside that references self. ie

class A(object):
  def __init__(self, name): 
    self.name=name

def my_name_is(self):
  print("my name is %s" %(self.name))

setattr(A, my_name_is.__name__, classmethod(my_name_is))
a = A('bob')
a.my_name_is() 

Because it tries to reference the name attr of 'A' rather than 'a'.

The other one is adding the function with a decorator ie something like a

@addMethod(A)
def say_hello_to(x):
  print("hello %s" %x)

rather some kind of equivalent to

def addMethod(cls, f) 
  setattr(cls, f.__name__, classmethod(f))

Answer 1

Question 1 : what you're looking for is a method, not classmethod . In this case, a simple assignment would work:

A.my_name_is = my_name_is

Question 2 : the expression following the @ should return a callable, ie addMethod(A) should be a callable. This can be done like this:

def addMethod(cls):
  def method_assigner(f):
     setattr(cls, f.__name__, f)
     return f
  return method_assigner

Then this works:

@addMethod(A)
def say_hello_to(x):
  print("hello %s" %x)

(In this example, x will get the value of self when say_hello_to is called. I'm not sure I understand exactly the role of x in your cas, but hopefully this makes it clear how to achieve what you want. Perhaps you want def say_hello_to(self, x):... ?).