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

Question

I want to use a decorator to handle auditing of various functions (mainly Django view functions, but not exclusively). In order to do this I would like to be able to audit the function post-execution - i.e. the function runs as normal, and if it returns without an exception, then the decorator logs the fact.

Something like:

@audit_action(action='did something') def do_something(*args, **kwargs):     if args[0] == 'foo':         return 'bar'     else:         return 'baz' 

Where audit_action would only run after the function has completed.

Answer 1

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After decorating, your do_something reference has been replaced by wrapper_func.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' 'bar'