Losing metadata

Python is a dynamic language that has some pretty neat introspective powers. For example, if you define a function with a docstring, that docstring is shown if you use the built-in help on your function:

def fibonacci(n):
    """Computes the recurrence relation F(n) = F(n - 1) + F(n - 2)."""
    if n < 2:
        return n
    return fibonacci(n - 1) + fibonacci(n - 2)

If you paste this code in the REPL and then type help(fibonacci), you should see something like the following:

Help on function fibonacci in module __main__:

fibonacci(n)
    Computes the recurrence relation F(n) = F(n - 1) + F(n - 2).
 Help on fibonacci line 1/4 (END) (press h for help or q to quit)

(Press q to close that help page.)

Note how the help message shows you the name of the function, the signature, and the docstring!

Now, go back and fetch the decorator timed_factory to apply it to your function fibonacci:

import time

def timed_factory(f):
    def timed_f(*args, **kwargs):
        start_time = time.perf_counter()
        result = f(*args, **kwargs)
        end_time = time.perf_counter()
        return result, end_time - start_time

    return timed_f


@timed_factory
def fibonacci(n):
    """Computes the recurrence relation F(n) = F(n - 1) + F(n - 2)."""
    if n < 2:
        return n
    return fibonacci(n - 1) + fibonacci(n - 2)

If you paste this code in the REPL and then type help(fibonacci), you will notice that you no longer get a nice help screen:

Help on function timed_f in module __main__:

timed_f(*args, **kwargs)
 Help on timed_factory.<locals>.timed_f line 1/3 (END) (press h for help or q to quit)

The problem is that the original function fibonacci was replaced by the wrapper timed_f from the decorator timed_factory, so help is now displaying help information about that… Which is technically correct, but not very helpful! Thankfully, there is a simple way of fixing this.