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 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Python不需要显式的指定变量和函数的类型"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "a = '1'  # a为str类型\n",
    "b = '2'  # b为str类型\n",
    "b = 3  # b可以被直接修改为int类型\n",
    "\n",
    "print(a+b)  # 报错：不同数据类型之间不能运算，说明python是强类型的\n",
    "\n",
    "# 函数定义也不需要声明返回值和参数的类型\n",
    "def plus(a, b):\n",
    "    return a+b"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Python的基础数据类型\n",
    "**注意：基础数据类型均为保留关键字，不要这些关键字作为变量名！**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "x = 1  # 合理\n",
    "print(int)\n",
    "int = 1  # 不合理但也不报错\n",
    "print(int)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 1.  整数类型（`int`）\n",
    "## 2. 浮点数类型（`float`）\n",
    "## 3. 布尔类型（`bool`）\n",
    "## 4. 列表类型（`list`）"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "my_list = [1, 2, 3, \"hello\"]\n",
    "print(type(my_list))  # 输出: <class 'list'>\n",
    "\n",
    "# 访问元素\n",
    "print(my_list[0])  # 输出: 1\n",
    "print(my_list[-1])  # 输出: \"hello\"\n",
    "print(my_list[0:2])  # 输出: [1, 2]，要头不要尾\n",
    "\n",
    "# 修改元素\n",
    "my_list[0] = 'modified'\n",
    "print(my_list)  # ['modified', 2, 3, \"hello\"]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 添加元素\n",
    "my_list.append('append')  \n",
    "print(\"my_list.append:\", my_list)  # ['modified', 2, 3, \"hello\", 'append']\n",
    "my_list.insert(1, 'insert')\n",
    "print(\"my_list.insert:\", my_list)  # ['modified', 'insert', 2, 3, \"hello\", 4]\n",
    "\n",
    "# 删除元素\n",
    "my_list.remove('modified')\n",
    "print(\"my_list.remove:\", my_list)  # ['insert', 2, 3, \"hello\", 4]\n",
    "my_list.pop(3)\n",
    "print(\"my_list.pop:\", my_list)  # ['insert', 2, 3, 4]\n",
    "\n",
    "# 查找元素\n",
    "print(\"2 in my_list:\")\n",
    "print(2 in my_list)  # 输出：True\n",
    "print(\"9 in my_list:\")\n",
    "print(9 in my_list)  # 输出：False\n",
    "print(\"my_list.index(2):\")\n",
    "print(my_list.index(2))  # 输出：1\n",
    "print(\"my_list.index(9):\")\n",
    "print(my_list.index(9))  # 直接抛异常"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 5. 字符串类型（`str`）"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "name = \"Python\"\n",
    "name = 'Python'  # 单引号和双引号在python里都表示字符串，没有任何区别"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 6. 元组类型（`tuple`）\n",
    "## 7. 集合类型（`set`）"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "my_set = {'one', 'two', 'three', 'three', 'four'}\n",
    "print(my_set)         # 输出: {'one', 'two', 'three', 'four'}?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "my_set.add('five')\n",
    "print(my_set)         # 输出: {'one', 'two', 'three', 'four', 'five'}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "my_set.remove('five')\n",
    "print(my_set)         # 输出: {'one', 'two', 'three', 'four'}?\n",
    "my_set.pop()\n",
    "print(my_set)         # 输出: {'two', 'three', 'four'}?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "print(my_set[0])  \t  # 直接报错：集合是无序的，不能按下标取值\n",
    "print('two' in my_set)  # 输出：True。集合通常就是这么用的，用来判断一个值在不在集合里。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 8. 字典类型（`dict`）\n",
    "键-值对的无序集合，且**键不可重复**。类似于哈希表。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [],
   "source": [
    "my_dict = {\"name\": \"Alice\", \"age\": 25}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 9. None 类型"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 条件控制语句\n",
    "## 1. 任何版本都通用：if语句"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [],
   "source": [
    "def positive_or_negative(a, b):\n",
    "    if a > 0:\n",
    "        print(\"It's positive.\")\n",
    "    if a == 0:\n",
    "        print(\"It's zero!\")\n",
    "    else:\n",
    "        print(\"It's negative.\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 下面是一段错误代码\n",
    "def describe_temperature(temp):\n",
    "    if temp >= 30:\n",
    "        print(\"It's a hot day!\")\n",
    "    if temp >= 20:\n",
    "        print(\"It's a warm day.\")\n",
    "    if temp >= 10:\n",
    "        print(\"It's a cool day.\")\n",
    "    else:\n",
    "        print(\"It's a cold day.\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 2. Python 3.10+ 新特性：match-case语句"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def fruit_description(fruit):\n",
    "    match fruit:\n",
    "        case \"apple\":\n",
    "            print(\"This is a red or green fruit, usually sweet.\")\n",
    "        case \"banana\":\n",
    "            print(\"This is a long, yellow fruit, and it is soft.\")\n",
    "        case \"orange\":\n",
    "            print(\"This is a round orange fruit, and it is juicy\")\n",
    "        case \"grape\":\n",
    "            print(\"This is a small fruit.\")\n",
    "        case _:\n",
    "            print(\"I don't know this fruit.\")"
   ]
  }
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