Python Decorators (similar to Java Annotations)

Why use Python Decorators

Python decorators is a wrapper around a python functions which allow you to

Validate the input arguments
Change the return result
Pass in additional input arguments
Perform open/lock before the function and close/unlock after the function
Allow you to execute code before and after the function
Conditionally execute the function

Basic Decorator

Add square bracket ([]) to the returned string.

from functools import wrapsdef my_decorator(f):    @wraps(f)    def wrapper(*args, **kwargs):       return "[{0}]".format(f(*args, **kwargs))    return wrapper

Test

@my_decoratordef hello(name):    return f"Hello, {name}"print(hello("Desmond"))

Output

[Hello, Desmond]

If you are sure of the fix named arguments of the target function, you can replace *args, **kwargs with actual named arguments:

from functools import wrapsdef my_decorator(f):    @wraps(f)    def wrapper(name):        return "[{0}]".format(f(name))    return wrapper

Decorator with Arguments

def my_decorator(str_format):    def decorator(f):        @wraps(f)        def wrapper(name):            return str_format.format(f(name))        '''        def wrapper(*args, **kwargs):            return str_format.format(f(*args, **kwargs))        '''        return wrapper    return decorator

Usage: pass the str_format into arguments

@my_decorator("<{0}>")def hello(name):    return f"Hello, {name}"

Decorator pass arguments to function

Besides manipulating the returned result, you can pass in additional arguments into the target function.

This decorator pass an age arguments into the target function.

def my_decorator(str_format):    def decorator(f):        @wraps(f)        def wrapper(name):            return str_format.format(f(name, age=10))        '''        def wrapper(*args, **kwargs):            return str_format.format(f(*args, **kwargs, age=10))        '''        return wrapper    return decorator

Test

@my_decorator("<{0}>")def hello(name, age):    return f"Hello, {name}. I'm {age} years old."print(hello("Desmond"))

Output

<Hello, Desmond. I'm 10 years old.>