Decorate a class in Python by defining the decorator as a class

Question

What is a simple example of decorating a class by defining the decorator as a class?

I'm trying to achieve what has been implemented in Python 2.6 using PEP 3129 except using classes not functions as Bruce Eckel explains here.

The following works:

class Decorator(object):     def __init__(self, arg):         self.arg = arg      def __call__(self, cls):         def wrappedClass(*args):             return cls(*args)         return type("TestClass", (cls,), dict(newMethod=self.newMethod, classattr=self.arg))      def newMethod(self, value):         return value * 2  @Decorator("decorated class") class TestClass(object):     def __init__(self):         self.name = "TestClass"         print "init %s"%self.name      def TestMethodInTestClass(self):         print "test method in test class"      def newMethod(self, value):         return value * 3 

Except, in the above, wrappedClass is not a class, but a function manipulated to return a class type. I would like to write the same callable as follows:

def __call__(self, cls):         class wrappedClass(cls):             def __init__(self):                 ... some code here ...         return wrappedClass 

How would this be done?

I'm not entirely sure what goes into """... some code here ..."""

Answer 1

If you want to overwrite new_method(), just do it:

class Decorator(object):     def __init__(self, arg):         self.arg = arg     def __call__(self, cls):         class Wrapped(cls):             classattr = self.arg             def new_method(self, value):                 return value * 2         return Wrapped  @Decorator("decorated class") class TestClass(object):     def new_method(self, value):         return value * 3 

If you don't want to alter __init__(), you don't need to overwrite it.