从入门到精通详解Python中的装饰器实战指南

@require_admin
def delete_user(user_id):
    # 删除用户的逻辑
    pass

def my_decorator(func):
    def wrapper(*args, **kwargs):
        print("函数执行前")
        result = func(*args, **kwargs)
        print("函数执行后")
        return result
    return wrapper

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

import time
import random

def retry(max_attempts=3, delay=1):
    def decorator(func):
        def wrapper(*args, **kwargs):
            for i in range(max_attempts):
                try:
                    return func(*args, **kwargs)
                except Exception as e:
                    if i == max_attempts - 1:
                        raise e
                    print(f"第 {i+1} 次尝试失败，正在重试...")
                    time.sleep(delay)
        return wrapper
    return decorator

# 使用方式：指定重试 3 次，每次间隔 1 秒
@retry(max_attempts=3, delay=1)
def unstable_api_call():
    if random.random() > 0.3:
        raise ValueError("API 不稳定")
    return "调用成功"

@my_decorator
def test():
    """这是一个测试函数"""
    pass

print(test.__name__)  # 输出：wrapper，而不是 test

from functools import wraps

def my_decorator(func):
    @wraps(func)  # <--- 加上这一行
    def wrapper(*args, **kwargs):
        return func(*args, **kwargs)
    return wrapper

def singleton(cls):
    instances = {}
    
    @wraps(cls)
    def get_instance(*args, **kwargs):
        if cls not in instances:
            instances[cls] = cls(*args, **kwargs)
        return instances[cls]
    
    return get_instance

@singleton
class DatabaseConnection:
    def __init__(self):
        print("正在建立数据库连接...")

# 测试
db1 = DatabaseConnection()
db2 = DatabaseConnection()
print(db1 is db2)  # 输出：True

from functools import lru_cache

@lru_cache(maxsize=128)
def fibonacci(n):
    if n < 2: return n
    return fibonacci(n-1) + fibonacci(n-2)
# 再次计算相同的 n 时，直接返回缓存值，速度极快

def validate_types(**types):
    def decorator(func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            # 这里可以实现具体的参数校验逻辑
            return func(*args, **kwargs)
        return wrapper
    return decorator

def heavy_init_decorator(func):
    print("装饰器初始化...") # 这一行在模块导入时就会执行
    return func

@decorator_A
@decorator_B
def my_func():
    pass