With this method decorator you can make a method a method container or -composition. See the included example to see how it works.

Python Composition Decorator

class composition(object):
    """This is a composition decorator, which allows a function to be used as a container for functions.
    On call, all the functions contained will be called.
    Keep in mind, though, that the decorated function itself won't be included/called.
    """
    class NoSuchElementError(Exception):
        def __init__(self):
            Exception.__init__(self, "You tried to remove an element from a composition that was not existent.")
    class ElementNotCallableError(Exception):
        def __init__(self):
            Exception.__init__(self, "You can only add callables to the composition")

    def __init__(self, func=None):
        self.functions = []
    def __call__(self):
        return_values = []
        for f in self.functions:
            return_values.append(f())
        return return_values
    def __add__(self, value):
        if not callable(value):
            raise ElementNotCallableError()
        self.functions.append(value)
        return self
    def __sub__(self, value):
        try:
            self.functions.remove(value)
        except ValueError:
            raise composition.NoSuchElementError()
        return self
    def removeLast(self):
        return self.functions.pop()
    def clear(self):
        self.functions = []


# Usage
class ExampleClass(object):
    @composition
    def onFocus(self):
        pass


# Test
def p(to_print="random string"):
    print to_print
def r(to_return=42):
    return to_return

c = ExampleClass()
c.onFocus += p
c.onFocus += lambda: p("second function call")
c.onFocus += r
return_values = c.onFocus()
print "---"
print "return values: "+str(return_values)