How does Python Decorator work?

By using decorators, you can add your own processing before or after the processing of existing functions. For example, you had

def decorator(func):
    def wrapper(*args, **kwargs):
        print('--decorator says hi--')
        func(*args, **kwargs)
        print('--decorator says bye--')
    return wrapper

@decorator
def test():
    print('Test function is executed')

test()

This program returns

--decorator says hi--
Test function is executed
--decorator says bye--