Decorator in Python

A good syntax sugar in python to improve the coding efficiency.

A good source for practicing Python decorator — ReaPython

Decorator

def decorator(func):
    def wrapper():
        print("Something is happening before the function is called.")
        func()
        print("Something is happening after the function is called.")
    return wrapper

def do_twice(func):
    def wrapper_do_twice():
        func()
        func()
    return wrapper_do_twice


@do_twice
def say_whee():
    print("Whee!")


print(say_whee())

But if we change the decorator

def decorator(func):
    def wrapper():
        print("Something is happening before the function is called.")
        func()
        print("Something is happening after the function is called.")
    return wrapper

def do_twice(func):
    def wrapper_do_twice():
        func()
        func()
    return wrapper_do_twice

@decorator
def say_whee():
    print("Whee!")

print(say_whee())

With Arguments

def greet(func):
    def wrapper_do_twice(*args, **kwargs):
        func(*args, **kwargs)
        func(*args, **kwargs)
    return wrapper_do_twice


@greet
def say_whee(name):
    print(f"Hola {name}")

print(say_whee("Python"))

Return values from decorated functions

def do_twice(func):
    def wrapper_do_twice(*args, **kwargs):
        func(*args, **kwargs)
        return func(*args, **kwargs)
    return wrapper_do_twice


@do_twice
def return_greeting(name):
    print("Creating greeting...")
    return f"Hey {name}!"

print(return_greeting("Hobbit"))

This does the same.

def do_twice(func):
    def wrapper_do_twice(*args, **kwargs):
        func(*args, **kwargs)
        return func(*args, **kwargs)
    return wrapper_do_twice


@do_twice
def return_greeting(name):
    print("Creating greeting...")
    return f"Hey {name}!"

hob = return_greeting("Hobbit")
print(hob)

Timing Function

import functools
import time

def decorator(func):
    @functools.wraps(func)
    def wrapper_decorator(*args, **kwargs):
        # Do something before
        value = func(*args, **kwargs)
        # Do something after
        return value
    return wrapper_decorator

def timer(func):
    # Print the runtime of the decorated function
    @functools.wraps(func)
    def wrapper_timer(*args, **kwargs):
        start_time = time.perf_counter()
        value = func(*args, **kwargs)
        end_time = time.perf_counter()
        run_time = end_time - start_time
        print(f"Finished {func.__name__}() in {run_time:.4f} secs")
        return value
    return wrapper_timer

@timer
def waste_some_time(num_times):
    for _ in range(num_times):
        sum([number**2 for number in range(10_000)])


waste_some_time(1)
# Finished waste_some_time() in 0.0010 secs

waste_some_time(999)
# Finished waste_some_time() in 0.3260 secs

Debug

import functools


def debug(func):
    # """Print the function signature and return value"""
    @functools.wraps(func)
    def wrapper_debug(*args, **kwargs):
        args_repr = [repr(a) for a in args]
        kwargs_repr = [f"{k}={repr(v)}" for k, v in kwargs.items()]
        signature = ", ".join(args_repr + kwargs_repr)
        print(f"Calling {func.__name__}({signature})")
        value = func(*args, **kwargs)
        print(f"{func.__name__}() returned {repr(value)}")
        return value

    return wrapper_debug


@debug
def make_greeting(name, age=None):
    if age is None:
        return f"Howdy {name}!"
    else:
        return f"Whoa {name}! {age} already, you're growing up!"

print(make_greeting("Benjamin"))
print(make_greeting("Juan", age=114))
print(make_greeting(name="Maria", age=116))