How can I get a Python decorator to run after the decorated function has completed?

Decorators usually return a wrapper function; just put your logic in the wrapper function after invoking the wrapped function.

def audit_action(action):
    def decorator_func(func):
        def wrapper_func(*args, **kwargs):
            # Invoke the wrapped function first
            retval = func(*args, **kwargs)
            # Now do something here with retval and/or action
            print('In wrapper_func, handling action {!r} after wrapped function returned {!r}'.format(action, retval))
            return retval
        return wrapper_func
    return decorator_func

So audit_action(action='did something') is a decorator factory that returns a scoped decorator_func, which is used to decorate your do_something (do_something = decorator_func(do_something)).

After decorating, your do_something reference has been replaced by wrapper_func. Calling wrapper_func() causes the original do_something() to be called, and then your code in the wrapper func can do things.

The above code, combined with your example function, gives the following output:

>>> do_something('foo')
In wrapper_func, handling action 'did something' after wrapped function returned 'bar'

Your decorator can handle it here itself, like

def audit_action(function_to_decorate):
    def wrapper(*args, **kw):
        # Calling your function
        output = function_to_decorate(*args, **kw)
        # Below this line you can do post processing
        print "In Post Processing...."
        return output
    return wrapper