Question

In python there are two ways to declare decorators:

Class based

class mydecorator(object):
    def __init__(self, f):
        self.f = f

    def __call__(self, *k, **kw):
        # before f actions
        self.f(*k, **kw)
        # after f actions

Function based

def mydecorator(f):
    def decorator(*k, **kw):
        # before f actions
        f(*k, **kw)
        # after f actions

    return decorator          

Is there any difference between these declarations?
In which cases each of them should be used?

Answer 1

If you want to keep state in the decorator you should use a class.

For example, this does not work

def mydecorator(f):
    x = 0 
    def decorator():
        x += 1 # x is a nonlocal name and cant be modified
        return f(x)
    return decorator 

There are many workarounds for this but the simplest way is to use a class

class mydecorator(object):
    def __init__(self, f):
        self.f = f
        self.x = 0

    def __call__(self, *k, **kw):
        self.x += 1
        return f(self.x)