Python 101: What are Python Decorators and How Do They Work?

What are Python Decorators and How Do They Work?

English Explanation:

Python decorators are a powerful tool to modify or extend the behavior of functions or methods. They are often used in scenarios such as:

Logging: Automatically log calls to functions.
Access Control: Restrict access to certain functions based on roles.
Instrumentation: Measure the time a function takes to execute.
Caching: Cache the result of function calls for optimization.

A decorator is simply a function that takes another function as an argument, adds some functionality before or after the execution of that function, and then returns a new function that wraps the original one.

Basic Example:

def my_decorator(func):
    def wrapper():
        print("Something before the function is called.")
        func()
        print("Something after the function is called.")
    return wrapper

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

say_hello()

Output:

Something before the function is called.
Hello!
Something after the function is called.

In this example, the decorator my_decorator adds behavior before and after the say_hello function is called.

Chinese Explanation:

Python装饰器是一种修改或扩展函数或方法行为的强大工具。它们常用于以下场景：

日志记录: 自动记录函数调用。
访问控制: 基于角色限制对某些函数的访问。
检测: 测量函数执行的时间。
缓存: 缓存函数调用结果以优化性能。

装饰器本质上是一个函数，它接受另一个函数作为参数，在该函数执行之前或之后添加一些功能，然后返回一个包装原始函数的新函数。

基础示例：

def my_decorator(func):
    def wrapper():
        print("在函数调用之前执行一些操作")
        func()
        print("在函数调用之后执行一些操作")
    return wrapper

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

say_hello()

输出：

在函数调用之前执行一些操作
你好!
在函数调用之后执行一些操作

在这个例子中，装饰器 my_decorator 在 say_hello 函数调用之前和之后添加了行为。

Warning:

English: Be careful with decorators that change the function’s signature (number of arguments). Always use functools.wraps to preserve the metadata (like the name and docstring) of the original function.
Chinese: 当使用装饰器时，要注意不要更改函数的签名（参数数量）。使用 functools.wraps 来保留原始函数的元数据（如名称和文档字符串）。

Key Points:

English: Decorators are functions that modify other functions.
Chinese: 装饰器是修改其他函数的函数。

Python Decorators in 1 Minute! by b001

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