What is the purpose of annotations with '@' in Python, and how do they work?

In Python, the '@' symbol is used for declaring decorators — special functions that modify the behavior of other functions or classes. The decorator is placed before the function or class definition and applies to that object.

A decorator takes a function (or class) as an argument, can modify or wrap it, and then returns a new function (or class).

Example:

def decorator(func):
    def wrapper(*args, **kwargs):
        print("Before function call")
        result = func(*args, **kwargs)
        print("After function call")
        return result
    return wrapper

@decorator
def say_hello():
    print("Hello!")

say_hello()

Output:

Before function call
Hello!
After function call

Thus, decorators with '@' allow for easy and readable modification of functions and classes' behavior.