decorators

Published 2025-05-13

A decorator is a function that takes another function as its argument and returns a new function that can incorporate the original function’s behavior and add functionality to it.

Timing decorator example:

def timing_decorator(f):

    @functools.wraps(f)
    def wrapper(*args, **kwargs):
        start = time.perf_counter()
        result = f(*args, **kwargs)
        print(f"Function {f.__name__} took {time.perf_counter() - start} seconds to execute.")
        return result

    return wrapper

@timing_decorator
def quick_function(n):
    """A sample function that does a quick computation."""
    result = sum(i*i for i in range(n))
    return f"Sum of squares up to {n-1} is {result}"

The decorator syntax:

@timing_decorator
def f():
  pass

is equivalent to:

f = timing_decorator(f)

timing_decorator returns the wrapper over the inputted function, which is closed over1 1. See the closures snippet. ↩ by the wrapper. Positional and keyword arguments to the function are passed to the wrapper, which can return the function’s output, a modified output, or something else altogether (such as wall time).

@functools.wraps(f) copies the metadata of f to the function it’s decorating. It’s used here because the metadata of f, including __name__ and __doc__, gets overridden by wrapper. Adding @functools.wraps(f) to the wrapper function therefore preserves f’s metadata.

print(f"Name of quick_function: {quick_function.__name__}")
# Output: Name of quick_function: quick_function
print(f"Docstring of quick_function: {quick_function.__doc__}")
# Output: Docstring of quick_function: A sample function that does a quick computation.