how can i define decorator method inside class? [duplicate]

Question

Possible Duplicate:
Can a class method be a decorator?

here's an example.

class myclass:     def __init__(self):         self.start = False      def check(self):         return not self.start      def doA(self):         if self.check():             return         print('A')      def doB(self):         if self.check():             return         print('B') 

as you see,i want to write the check action in a decorator way, but after i tried many times, i found i can only write the method outside my class.please teach me how to write it inside the class ,thanks

edit:

i can write the code in this way:

def check(func):     def checked(self):         if not self.start:             return         func(self)     return checked  class myclass:     def __init__(self):         self.start = False      @check     def doA(self):         print('A')      @check     def doB(self):         print('B')   a = myclass()  a.doA() a.doB()  a.start = True  a.doA() a.doB() 

but i don't think it's a good practice, i want to defined the check method inside my class.

Answer 1

While I don't think this is completely needed all the time, here is how you would make a decorator within your class. It is a little more cumbersome because of the way the methods become bound to the self later on. Normally with plain function decorators you don't have to worry about that.

The requirements are:

1. The decorator needs to be defined first before the methods that will use it
2. It needs to use functools.wraps to preserve the bound methods properly

Example:

from functools import wraps  class myclass:     def __init__(self):         self.start = False      def _with_check(f):         @wraps(f)         def wrapped(inst, *args, **kwargs):             if inst.check():                 return             return f(inst, *args, **kwargs)         return wrapped      def check(self):         return self.start      @_with_check     def doA(self):         print('A')      @_with_check     def doB(self):         print('B') 

I made it a protected member since it is not really something someone else needs to use outside of the class. And it still preserves your public check() call for use by itself. The decorator simply wraps calling it first before calling the target method.