PyLzuCSEdu/4 装饰器-知识版.ipynb

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  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 函数装饰器\n",
    "\n",
    "装饰器（Decorator）是 Python 中一个非常重要的概念，装饰器在不修改原函数代码的情况下，给原函数动态地增加功能。\n",
    "\n",
    "装饰器本质上是一个高阶函数，它接受一个函数作为参数并返回一个新的函数。\n",
    "\n",
    "装饰器的常见用途：日志记录、性能测试、权限验证、缓存、事务处理等\n",
    "\n",
    "装饰器是 Python 中非常强大的特性，合理使用可以让代码更加简洁、优雅，并且符合 DRY（Don't Repeat Yourself）原则。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 一、基本语法"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 基本装饰器"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "执行前\n",
      "Hello!\n",
      "执行后\n"
     ]
    }
   ],
   "source": [
    "def my_decorator(func):\n",
    "    def wrapper():\n",
    "        print(\"执行前\")\n",
    "        func()\n",
    "        print(\"执行后\")\n",
    "    return wrapper\n",
    "\n",
    "@my_decorator\n",
    "def say_hello():\n",
    "    print(\"Hello!\")\n",
    "\n",
    "# 调用函数\n",
    "say_hello()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 带参数的装饰器"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "执行前\n",
      "执行后\n",
      "8\n",
      "执行前\n",
      "执行后\n",
      "ChinaLanzhou\n"
     ]
    }
   ],
   "source": [
    "def my_decorator(func):\n",
    "    def wrapper(*args, **kwargs):\n",
    "        print(\"执行前\")\n",
    "        result = func(*args, **kwargs)\n",
    "        print(\"执行后\")\n",
    "        return result\n",
    "    return wrapper\n",
    "\n",
    "@my_decorator\n",
    "def add(a, b):\n",
    "    return a + b\n",
    "\n",
    "# 调用函数\n",
    "print(add(3, 5))\n",
    "print(add('China', 'Lanzhou'))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 装饰器带参数"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "你好，小明!\n",
      "你好，小明!\n",
      "你好，小明!\n"
     ]
    }
   ],
   "source": [
    "def repeat(times):\n",
    "    def decorator(func):\n",
    "        def wrapper(*args, **kwargs):\n",
    "            for _ in range(times):\n",
    "                result = func(*args, **kwargs)\n",
    "            return result\n",
    "        return wrapper\n",
    "    return decorator\n",
    "\n",
    "@repeat(3)\n",
    "def greet(name):\n",
    "    print(f\"你好，{name}!\")\n",
    "\n",
    "# 调用函数\n",
    "greet(\"小明\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 二、语法设计动机"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "装饰器的基本语法如下\n",
    "\n",
    "<code>\n",
    "@decorator\n",
    "def function_to_decorate(*args, **kwargs):\n",
    "    # 函数体        \n",
    "</code>    \n",
    "\n",
    "这等同于：\n",
    "<code>\n",
    "def function_to_decorate(*args, **kwargs):\n",
    "    # 函数体    \n",
    "function_to_decorate = decorator(function_to_decorate)\n",
    "</code>    "
   ]
  },
  {
   "cell_type": "raw",
   "metadata": {},
   "source": [
    "在下面例子中，uppercase_decorator 接受一个函数 func 作为参数，并返回一个新的函数 wrapper。\n",
    "wrapper 函数将 func 的结果转换为大写。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "HELLO, ALICE!\n"
     ]
    }
   ],
   "source": [
    "# 高阶函数的写法\n",
    "\n",
    "def greet(name):\n",
    "    return f\"Hello, {name}!\"\n",
    "\n",
    "def uppercase_decorator(func):\n",
    "    def wrapper(name):\n",
    "        result = func(name)\n",
    "        return result.upper()\n",
    "    return wrapper\n",
    "\n",
    "greet_uppercase = uppercase_decorator(greet)\n",
    "print(greet_uppercase(\"Alice\"))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "HELLO, ALICE!\n"
     ]
    }
   ],
   "source": [
    "# 装饰器的写法\n",
    "\n",
    "def uppercase_decorator(func):\n",
    "    def wrapper(name):\n",
    "        result = func(name)\n",
    "        return result.upper()\n",
    "    return wrapper\n",
    "\n",
    "@uppercase_decorator\n",
    "def greet(name):\n",
    "    return f\"Hello, {name}!\"\n",
    "\n",
    "print(greet(\"Alice\"))"
   ]
  },
  {
   "cell_type": "raw",
   "metadata": {},
   "source": [
    "在这个例子中，@uppercase_decorator 等价于 greet = uppercase_decorator(greet)。\n",
    "使用装饰器，结构更清楚，使用更方便。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 三、应用"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "函数执行完毕\n",
      "函数 slow_function 执行时间：1.0016472339630127秒\n"
     ]
    }
   ],
   "source": [
    "# 一个简单的计时装饰器\n",
    "\n",
    "import time\n",
    "\n",
    "def timer(func):\n",
    "    def wrapper(*args, **kwargs):\n",
    "        start = time.time()\n",
    "        result = func(*args, **kwargs)\n",
    "        end = time.time()\n",
    "        print(f\"函数 {func.__name__} 执行时间：{end - start}秒\")\n",
    "        return result\n",
    "    return wrapper\n",
    "\n",
    "@timer\n",
    "def slow_function():\n",
    "    time.sleep(1)\n",
    "    print(\"函数执行完毕\")\n",
    "\n",
    "# 调用函数\n",
    "slow_function()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'<b><i> hello china 2025 </i></b>'"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "###  一个标记文本生成工具\n",
    "\n",
    "def make_bold(fn): \n",
    "    def inner(s): return  \"<b>\" + fn(s) + \"</b>\" \n",
    "    return inner\n",
    "def make_italic(fn): \n",
    "    def inner(s): return  \"<i>\" + fn(s) + \"</i>\" \n",
    "    return inner\n",
    "\n",
    "@make_bold\n",
    "@make_italic\n",
    "def hello(s) : return s\n",
    "\n",
    "hello( ' hello china 2025 ')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 其它\n",
    "\n",
    "- 当有多个装饰器时,装饰器的执行顺序是**从下到上**\n",
    "- Python 内置了很多实用的装饰器，如 @property、@staticmethod、@classmethod 等\n",
    "- 装饰器也可以使用类创建"
   ]
  }
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