What are decorators in Python and can you provide some examples?

What are decorators in Python and can you provide some examples?

Decorators in Python are functions that modify the behavior of another function. They are often used for logging, access control, and instrumentation. Here's a simple example:

def my_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

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

say_hello()

In this example, my_decorator wraps the say_hello function, adding behavior before and after its execution.

Can you explain how to use multiple decorators on a single function?

Certainly! You can stack multiple decorators on a single function by placing them one above the other. Here's an example:

def decorator_one(func):
    def wrapper():
        print("Decorator One: Before the function.")
        func()
        print("Decorator One: After the function.")
    return wrapper


def decorator_two(func):
    def wrapper():
        print("Decorator Two: Before the function.")
        func()
        print("Decorator Two: After the function.")
    return wrapper

@decorator_one
@decorator_two
def say_hello():
    print("Hello!")

say_hello()

In this case, say_hello will be wrapped by both decorators, executing them in the order they are applied.

What are some common use cases for decorators?

Common use cases for decorators include:

1. Logging: Automatically log function calls and their parameters.
2. Access Control: Restrict access to certain functions based on user permissions.
3. Caching: Store results of expensive function calls to improve performance.
4. Timing: Measure the execution time of functions for performance analysis.

Can you show me an example of a decorator for logging?

Sure! Here's a simple logging decorator:

import logging

logging.basicConfig(level=logging.INFO)

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

@log_decorator
def add(a, b):
    return a + b

add(5, 3)

This decorator logs when the function is called and when it finishes.