Explain what the decorator pattern in Python is and how to apply it.

The decorator pattern in Python is a way to dynamically extend the functionality of a function or method without changing their original code. A decorator is a function that takes another function and returns a new function with additional behavior.

Usage:

• Allows adding logging, permission checks, caching, and other aspects without code duplication.
• Used with the syntax @decorator above the function definition.

Example:

def decorator(func):
    def wrapper(*args, **kwargs):
        print(f"Calling function {func.__name__}")
        result = func(*args, **kwargs)
        print(f"Function {func.__name__} finished")
        return result
    return wrapper

@decorator
def say_hello(name):
    print(f"Hello, {name}!")

say_hello("World")

In this example, when calling say_hello, it first outputs a message about the start of the call, then executes the function itself, and afterwards outputs a message about completion.