I have an issue with using a class to decorate another class' method. Code is as follows:
class decorator(object):
def __init__(self, func):
self.func = func
def __call__(self, *args):
return self.func(*args)
class test(object):
@decorator
def func(self, x, y):
print x, y
t = test()
t.func(1, 2)
It shows this error
TypeError: func() takes exactly 3 arguments (2 given).
If called using:
t.func(t, 1, 2)
then it passes. But then if the decorator is taken away, then this line will have issue again.
Why this is happening and how to solve it?
Edit: second version of the code to show the self in decorator.__call__ should be different than the self in test.func:
class decorator(object):
def __init__(self, func):
self.func = func
def __call__(self, *args):
return self.func(*args)
class test(object):
def __init__(self):
self.x = 1
self.y = 2
@decorator
def func(self):
print self
print self.x, self.y
t = test()
t.func()
This shows the same error. But
t.func(t)
works but not ideal.
To work as a method, an object in a class needs to implement part of the descriptor protocol. That is, it should have a __get__ method that returns a callable object which has been "bound" to the instance the method was looked up on.
Here's one way that you could make that work, using a wrapper function:
class decorator(object):
def __init__(self, func):
self.func = func
def __get__(self, instance, owner):
def wrapper(*args):
return self.func(instance, *args) # note, self here is the descriptor object
return wrapper
You could instead return an instance of some other class from __get__, rather than a function, and use the __call__ method of that other class to implement the wrapper. If you're not using a closure though, you'd need to pass the instance to the wrapper class explicitly (as well as the function, since self.func won't work outside the descriptor class).