{ "cells": [ { "cell_type": "markdown", "id": "b0217281", "metadata": {}, "source": [ "# 第 3 讲｜Python 流程控制：条件判断与循环\n", "\n", "**对象：** 已会变量、输入输出、比较和逻辑运算的 Python 初学者。 \n", "**课堂目标：** 用条件语句做选择，用循环完成重复任务，并能在合适时结束或跳过循环。 \n", "**参考：** Python 快速编程入门（第 3 版）第 3 章，参考文件 3f.pdf。\n", "\n", "本课以固定样例演示，避免课堂中等待键盘输入；课后练习再把规则补完整。\n", "\n", "> **课堂节奏：** 每个知识点先运行“课堂演示（样本代码）”，再由学生在紧随其后的“课堂练习（学生填写）”中补全答案。" ] }, { "cell_type": "markdown", "id": "539ac900", "metadata": {}, "source": [ "## 1. 流程控制先回答三个问题\n", "\n", "1. 条件成立时做什么，不成立时做什么？\n", "2. 哪件事需要重复做？重复到什么时候？\n", "3. 什么时候应当提前结束，或跳过本轮？\n", "\n", "条件表达式会得到 True 或 False。if 会根据这个结果决定是否执行缩进的代码块。" ] }, { "cell_type": "markdown", "id": "fe688fc2", "metadata": {}, "source": [ "### 课堂演示（样本代码）\n", "\n", "先由教师运行下方样本代码，观察条件、循环变量和输出如何变化。" ] }, { "cell_type": "code", "execution_count": 1, "id": "24cce307", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.532543Z", "iopub.status.busy": "2026-07-26T07:23:08.532371Z", "iopub.status.idle": "2026-07-26T07:23:08.538754Z", "shell.execute_reply": "2026-07-26T07:23:08.538273Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "分数： 58\n", "是否及格： False\n" ] } ], "source": [ "score = 58\n", "print(\"分数：\", score)\n", "print(\"是否及格：\", score >= 60)" ] }, { "cell_type": "markdown", "id": "41c4af29", "metadata": {}, "source": [ "### 课堂练习（学生填写）\n", "\n", "根据刚才的样本代码独立补全下方空位；完成后再运行并检查结果。" ] }, { "cell_type": "code", "execution_count": 3, "id": "f8aef43f", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.541177Z", "iopub.status.busy": "2026-07-26T07:23:08.541016Z", "iopub.status.idle": "2026-07-26T07:23:08.543035Z", "shell.execute_reply": "2026-07-26T07:23:08.542750Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "60.0\n" ] } ], "source": [ "# 目标：预测条件结果，并补全成立时的输出。\n", "score = 40\n", "# print(score >= 60)\n", "if score < 60:\n", " # 请填写输出语句\n", " print(score*1.5)" ] }, { "cell_type": "markdown", "id": "f1231da9", "metadata": {}, "source": [ "## 2. if：条件成立才进入缩进代码块\n", "\n", " if score >= 60:\n", " print(\"考试及格\")\n", "\n", "冒号标记条件开始；缩进决定哪些语句属于这个分支。" ] }, { "cell_type": "markdown", "id": "1f99994f", "metadata": {}, "source": [ "### 课堂演示（样本代码）\n", "\n", "先由教师运行下方样本代码，观察条件、循环变量和输出如何变化。" ] }, { "cell_type": "code", "execution_count": 7, "id": "0d1e6e63", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.544758Z", "iopub.status.busy": "2026-07-26T07:23:08.544618Z", "iopub.status.idle": "2026-07-26T07:23:08.547381Z", "shell.execute_reply": "2026-07-26T07:23:08.547014Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "分数： 58\n", "本次评估结束\n", "\n", "分数： 88\n", "考试及格\n", "本次评估结束\n" ] } ], "source": [ "score = 58\n", "print(\"分数：\", score)\n", "if score >= 60:\n", " print(\"考试及格\")\n", "print(\"本次评估结束\")\n", "\n", "print()\n", "score = 88\n", "print(\"分数：\", score)\n", "if score >= 60:\n", " print(\"考试及格\")\n", "print(\"本次评估结束\")" ] }, { "cell_type": "markdown", "id": "623bd8a9", "metadata": {}, "source": [ "### 课堂练习（学生填写）\n", "\n", "根据刚才的样本代码独立补全下方空位；完成后再运行并检查结果。" ] }, { "cell_type": "code", "execution_count": 4, "id": "9d0d8e98", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.549771Z", "iopub.status.busy": "2026-07-26T07:23:08.549599Z", "iopub.status.idle": "2026-07-26T07:23:08.551489Z", "shell.execute_reply": "2026-07-26T07:23:08.551202Z" } }, "outputs": [], "source": [ "# 目标：分别测试 55 分和 75 分，观察 if 只处理条件成立的情况。\n", "# score = 55\n", "# if score >= 60:\n", "# print(\"考试及格\")\n", "#\n", "# score = 75\n", "# if score >= 60:\n", "# # 请填写输出语句" ] }, { "cell_type": "markdown", "id": "71c22623", "metadata": {}, "source": [ "## 3. if-else：两种结果都要处理\n", "\n", "当规则覆盖成立和不成立两种情况时，用 else 保证程序都有反馈。\n", "\n", "下面会用到上一阶段已学过的函数：\n", "\n", "- def 函数名(参数)：定义一段可重复调用的代码；\n", "- return 结果：把函数计算的结果交回给调用处。" ] }, { "cell_type": "code", "execution_count": null, "id": "d1d6ed34", "metadata": {}, "outputs": [ { "data": { "text/plain": [ "39" ] }, "execution_count": 13, "metadata": {}, "output_type": "execute_result" } ], "source": [ "def add(a,b):\n", " return a+b\n", "\n", "results = add(6,4)\n", "\n", "results*5+4" ] }, { "cell_type": "markdown", "id": "a9f87a2e", "metadata": {}, "source": [ "### 课堂演示（样本代码）\n", "\n", "先由教师运行下方样本代码，观察条件、循环变量和输出如何变化。" ] }, { "cell_type": "code", "execution_count": 14, "id": "7c8bb825", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.553056Z", "iopub.status.busy": "2026-07-26T07:23:08.552916Z", "iopub.status.idle": "2026-07-26T07:23:08.555540Z", "shell.execute_reply": "2026-07-26T07:23:08.555113Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "59 -> 不及格\n" ] } ], "source": [ "def pass_or_fail(score):\n", " if score >= 60:\n", " return \"及格\"\n", " else:\n", " return \"不及格\"\n", "\n", "# 和下面的函数等价： \n", "# def pass_or_fail(score):\n", "# if score >= 60:\n", "# return \"及格\"\n", "# return \"不及格\"\n", "\n", "\n", "print(59, \"->\", pass_or_fail(59))\n", "# print(60, \"->\", pass_or_fail(60))\n", "# print(100, \"->\", pass_or_fail(100))" ] }, { "cell_type": "code", "execution_count": null, "id": "98625720", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "及格\n" ] } ], "source": [ "results = pass_or_fail(60)" ] }, { "cell_type": "markdown", "id": "58fe9557", "metadata": {}, "source": [ "### 课堂练习（学生填写）\n", "\n", "根据刚才的样本代码独立补全下方空位；完成后再运行并检查结果。" ] }, { "cell_type": "code", "execution_count": null, "id": "254333d2", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.557785Z", "iopub.status.busy": "2026-07-26T07:23:08.557626Z", "iopub.status.idle": "2026-07-26T07:23:08.559440Z", "shell.execute_reply": "2026-07-26T07:23:08.559166Z" } }, "outputs": [], "source": [ "# 目标：补全函数，使其返回及格或不及格。\n", "# def pass_or_fail(score):\n", "# if score < 60:\n", "# return # 请填写\n", "# else:\n", "# return # 请填写\n", "\n", "# print(pass_or_fail(58))" ] }, { "cell_type": "markdown", "id": "69601f47", "metadata": {}, "source": [ "## 4. if-elif-else：多分支按顺序匹配\n", "\n", "高分阈值必须先判断。分支一旦命中，后续 elif 和 else 不再执行。\n", "\n", "- 大于等于 85：优秀\n", "- 大于等于 75：良好\n", "- 大于等于 60：中等\n", "- 其他：差" ] }, { "cell_type": "code", "execution_count": null, "id": "4bd2e8e9", "metadata": {}, "outputs": [], "source": [] }, { "cell_type": "markdown", "id": "6dec4ff1", "metadata": {}, "source": [ "### 课堂演示（样本代码）\n", "\n", "先由教师运行下方样本代码，观察条件、循环变量和输出如何变化。" ] }, { "cell_type": "code", "execution_count": 18, "id": "a4511e59", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.561039Z", "iopub.status.busy": "2026-07-26T07:23:08.560913Z", "iopub.status.idle": "2026-07-26T07:23:08.564465Z", "shell.execute_reply": "2026-07-26T07:23:08.563977Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "59 -> 差\n", "60 -> 中等\n", "74 -> 中等\n", "75 -> 良好\n", "84 -> 良好\n", "85 -> 优秀\n" ] } ], "source": [ "def grade(score):\n", " if score >= 85:\n", " return \"优秀\"\n", " elif score >= 75:\n", " return \"良好\"\n", " elif score >= 60:\n", " return \"中等\"\n", " else:\n", " return \"差\"\n", "\n", "\n", "print(59, \"->\", grade(59))\n", "print(60, \"->\", grade(60))\n", "print(74, \"->\", grade(74))\n", "print(75, \"->\", grade(75))\n", "print(84, \"->\", grade(84))\n", "print(85, \"->\", grade(85))" ] }, { "cell_type": "code", "execution_count": 1, "id": "b2fae478", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "a\n" ] } ], "source": [ "print(\"a\")" ] }, { "cell_type": "code", "execution_count": 2, "id": "62e2cc78", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "a b\n" ] } ], "source": [ "print(\"a\",\"b\")" ] }, { "cell_type": "markdown", "id": "84bdb659", "metadata": {}, "source": [ "### 课堂练习（学生填写）\n", "\n", "根据刚才的样本代码独立补全下方空位；完成后再运行并检查结果。" ] }, { "cell_type": "code", "execution_count": 8, "id": "8009f137", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.566557Z", "iopub.status.busy": "2026-07-26T07:23:08.566416Z", "iopub.status.idle": "2026-07-26T07:23:08.568338Z", "shell.execute_reply": "2026-07-26T07:23:08.568075Z" } }, "outputs": [], "source": [ "# 目标：按 >=85、>=75、>=60、其他的规则补全等级函数。\n", "# def grade(score):\n", "# # 请填写 if、elif、else 分支\n", "# return \"请修改\"\n", "#\n", "# print(grade(75))" ] }, { "cell_type": "code", "execution_count": 5, "id": "196584ee", "metadata": {}, "outputs": [ { "data": { "text/plain": [ "'语文优秀'" ] }, "execution_count": 5, "metadata": {}, "output_type": "execute_result" } ], "source": [ "def grade(score:int, subject:str) -> str:\n", " if score >= 85:\n", " if subject == \"语文\":\n", " return \"语文优秀\"\n", " else:\n", " return \"优秀\"\n", " elif score >= 75:\n", " return \"良好\"\n", " elif score >= 60:\n", " return \"中等\"\n", " else:\n", " return \"差\"\n", "\n", "grade(98, \"语文\")" ] }, { "cell_type": "markdown", "id": "21686bd8", "metadata": {}, "source": [ "## 5. 条件嵌套：只有外层成立，才检查内层\n", "\n", "计算某月天数时，先按月份分类；只有 2 月才需要判断闰年。\n", "闰年规则：能被 400 整除，或能被 4 整除但不能被 100 整除。\n", "\n", "本例对非法月份直接返回一段提示文本，不额外引入异常处理。" ] }, { "cell_type": "markdown", "id": "c89a7b4d", "metadata": {}, "source": [ "### 课堂演示（样本代码）\n", "\n", "先由教师运行下方样本代码，观察条件、循环变量和输出如何变化。" ] }, { "cell_type": "code", "execution_count": 7, "id": "2c99e0e9", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.570053Z", "iopub.status.busy": "2026-07-26T07:23:08.569930Z", "iopub.status.idle": "2026-07-26T07:23:08.573636Z", "shell.execute_reply": "2026-07-26T07:23:08.573199Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "2025 年 3 月： 31\n" ] } ], "source": [ "# def days_in_month(year, month):\n", "# if (month == 1 or month == 3 or month == 5 or month == 7 \n", "# or month == 8 or month == 10 or month == 12):\n", "# return 31\n", "# elif month == 4 or month == 6 or month == 9 or month == 11:\n", "# return 30\n", "# elif month == 2:\n", "# # 这一年是不是闰年\n", "# is_leap = year % 400 == 0 \n", "# if is_leap:\n", "# return 29\n", "# return 28\n", "# else:\n", "# return \"月份必须在 1 到 12 之间\"\n", "\n", "def days_in_month(year, month):\n", " if month in [1,3,5,7,8,10,12]:\n", " return 31\n", " elif month in [4,6,9,11]:\n", " return 30\n", " elif month == 2:\n", " # 这一年是不是闰年\n", " is_leap = year % 400 == 0 \n", " if is_leap:\n", " return 29\n", " return 28\n", " else:\n", " return \"月份必须在 1 到 12 之间\"\n", "\n", "\n", "# print(\"2024 年 2 月：\", days_in_month(2024, 2))\n", "# print(\"2023 年 2 月：\", days_in_month(2023, 2))\n", "print(\"2025 年 3 月：\", days_in_month(2025, 3))" ] }, { "cell_type": "code", "execution_count": 8, "id": "f7409704", "metadata": {}, "outputs": [ { "data": { "text/plain": [ "True" ] }, "execution_count": 8, "metadata": {}, "output_type": "execute_result" } ], "source": [ "7 in [1,3,5,7,8,10,12]" ] }, { "cell_type": "markdown", "id": "d3c4afd6", "metadata": {}, "source": [ "### 课堂练习（学生填写）\n", "\n", "根据刚才的样本代码独立补全下方空位；完成后再运行并检查结果。" ] }, { "cell_type": "code", "execution_count": 10, "id": "24a5a93a", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.575552Z", "iopub.status.busy": "2026-07-26T07:23:08.575398Z", "iopub.status.idle": "2026-07-26T07:23:08.577323Z", "shell.execute_reply": "2026-07-26T07:23:08.576967Z" } }, "outputs": [], "source": [ "# 目标：补全 2 月的天数判断；只返回 29 或 28。\n", "# year = 2024\n", "# is_leap = year % 400 == 0 or (\n", "# year % 4 == 0 and year % 100 != 0\n", "# )\n", "# if is_leap:\n", "# days = # 请填写\n", "# else:\n", "# days = # 请填写\n", "# print(days)" ] }, { "cell_type": "markdown", "id": "037491e9", "metadata": {}, "source": [ "## 6. while：条件为真就继续\n", "\n", "while 适合不知道要执行多少次、但知道何时停止的任务。\n", "循环中必须改变参与条件的变量，否则可能无法停止。" ] }, { "cell_type": "markdown", "id": "cff89d96", "metadata": {}, "source": [ "### 课堂演示（样本代码）\n", "\n", "先由教师运行下方样本代码，观察条件、循环变量和输出如何变化。" ] }, { "cell_type": "code", "execution_count": 10, "id": "d8e6c9ee", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.579116Z", "iopub.status.busy": "2026-07-26T07:23:08.578946Z", "iopub.status.idle": "2026-07-26T07:23:08.581528Z", "shell.execute_reply": "2026-07-26T07:23:08.581087Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "1 到 20 的和： 210\n", "循环结束时 current： 21\n" ] } ], "source": [ "current = 1\n", "total = 0\n", "while current <= 20:\n", " total += current\n", " current += 1\n", "\n", "print(\"1 到 20 的和：\", total)\n", "print(\"循环结束时 current：\", current)" ] }, { "cell_type": "markdown", "id": "cd9744ff", "metadata": {}, "source": [ "### 课堂练习（学生填写）\n", "\n", "根据刚才的样本代码独立补全下方空位；完成后再运行并检查结果。" ] }, { "cell_type": "code", "execution_count": 12, "id": "71db2916", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.583441Z", "iopub.status.busy": "2026-07-26T07:23:08.583296Z", "iopub.status.idle": "2026-07-26T07:23:08.585109Z", "shell.execute_reply": "2026-07-26T07:23:08.584850Z" } }, "outputs": [], "source": [ "# 目标：使用 while 计算 1 到 5 的和。\n", "# current = 1\n", "# total = 0\n", "# while current <= 5:\n", "# # 请填写累加和更新\n", "# #\n", "# print(total)" ] }, { "cell_type": "markdown", "id": "d1fb9d95", "metadata": {}, "source": [ "## 7. for 与 range：逐个访问，次数清楚\n", "\n", "for 适合遍历字符串、列表等对象。range(stop) 产生 0 到 stop-1；\n", "range(start, stop) 产生 start 到 stop-1。右边界不包含在结果中。" ] }, { "cell_type": "code", "execution_count": 15, "id": "49cdf74a", "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[0, 1, 2]" ] }, "execution_count": 15, "metadata": {}, "output_type": "execute_result" } ], "source": [ "list(range(3)) " ] }, { "cell_type": "code", "execution_count": 14, "id": "3eb84b6b", "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[3, 4, 5, 6, 7, 8]" ] }, "execution_count": 14, "metadata": {}, "output_type": "execute_result" } ], "source": [ "list(range(3,9))" ] }, { "cell_type": "markdown", "id": "e6ff64a9", "metadata": {}, "source": [ "### 课堂演示（样本代码）\n", "\n", "先由教师运行下方样本代码，观察条件、循环变量和输出如何变化。" ] }, { "cell_type": "code", "execution_count": 25, "id": "aff07d7a", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.586708Z", "iopub.status.busy": "2026-07-26T07:23:08.586560Z", "iopub.status.idle": "2026-07-26T07:23:08.589212Z", "shell.execute_reply": "2026-07-26T07:23:08.588717Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "遍历字符串：\n", "P\n", "y\n", "t\n", "h\n", "o\n", "n\n" ] } ], "source": [ "print(\"遍历字符串：\")\n", "for letter in \"Python\":\n", " print(letter)" ] }, { "cell_type": "code", "execution_count": 28, "id": "065d9061", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "遍历列表：\n", "0\n", "4\n", "8\n", "12\n", "8.4\n" ] } ], "source": [ "print(\"遍历列表：\")\n", "for element in [0,1,2,3,2.1]:\n", " print(element*4)" ] }, { "cell_type": "code", "execution_count": 29, "id": "96dc4c01", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "\n", "\n", "range(2, 6)：\n", "2 3 4 5 " ] } ], "source": [ "print(\"\\n\\nrange(2, 6)：\")\n", "for number in range(2, 6):\n", " print(number, end=\" \")" ] }, { "cell_type": "code", "execution_count": 32, "id": "e0975f0e", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "\n", "\n", "range(2, 6)：\n", "2 3 4 5 " ] } ], "source": [ "print(\"\\n\\nrange(2, 6)：\")\n", "for number in [2,3,4,5]:\n", " print(number, end=\" \")" ] }, { "cell_type": "markdown", "id": "eddef966", "metadata": {}, "source": [ "### 课堂练习（学生填写）\n", "\n", "根据刚才的样本代码独立补全下方空位；完成后再运行并检查结果。" ] }, { "cell_type": "code", "execution_count": 14, "id": "f7523315", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.591317Z", "iopub.status.busy": "2026-07-26T07:23:08.591092Z", "iopub.status.idle": "2026-07-26T07:23:08.593097Z", "shell.execute_reply": "2026-07-26T07:23:08.592813Z" } }, "outputs": [], "source": [ "# 目标：使用 range(1, 6) 输出 1 到 5。\n", "# for number in range(1, 6):\n", "# # 请填写输出语句\n", "# #" ] }, { "cell_type": "markdown", "id": "90a5a59b", "metadata": {}, "source": [ "## 8. 循环嵌套：外层控制行，内层控制列\n", "\n", "输出棋盘、乘法表、二维数据时，经常需要两层循环。\n", "先说清每层的职责，再写代码。\n", "\n", "print(内容, end=\" \") 会让下一次输出仍留在同一行；不写 end 时，print 默认会在输出后换行。" ] }, { "cell_type": "markdown", "id": "5c29746e", "metadata": {}, "source": [ "### 课堂演示（样本代码）\n", "\n", "先由教师运行下方样本代码，观察条件、循环变量和输出如何变化。" ] }, { "cell_type": "code", "execution_count": 15, "id": "6080368c", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.594708Z", "iopub.status.busy": "2026-07-26T07:23:08.594578Z", "iopub.status.idle": "2026-07-26T07:23:08.597239Z", "shell.execute_reply": "2026-07-26T07:23:08.596900Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "+ - + - + \n", "- + - + - \n", "+ - + - + \n", "- + - + - \n", "+ - + - + \n" ] } ], "source": [ "def draw_board(size):\n", " for row in range(size):\n", " for col in range(size):\n", " if (row + col) % 2 == 0:\n", " print(\"+\", end=\" \")\n", " else:\n", " print(\"-\", end=\" \")\n", " print()\n", "\n", "\n", "draw_board(5)" ] }, { "cell_type": "code", "execution_count": 2, "id": "0546cd37", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "+ - + \n", "- + - \n" ] } ], "source": [ "def draw_board(a,b):\n", " for row in range(a):\n", " for col in range(b):\n", " if (row + col) % 2 == 0:\n", " print(\"+\", end=\" \")\n", " else:\n", " print(\"-\", end=\" \")\n", " print()\n", "\n", "\n", "draw_board(2,3)" ] }, { "cell_type": "markdown", "id": "f8914c6c", "metadata": {}, "source": [ "### 课堂练习（学生填写）\n", "\n", "根据刚才的样本代码独立补全下方空位；完成后再运行并检查结果。" ] }, { "cell_type": "code", "execution_count": 2, "id": "5b78003c", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.599585Z", "iopub.status.busy": "2026-07-26T07:23:08.599406Z", "iopub.status.idle": "2026-07-26T07:23:08.601252Z", "shell.execute_reply": "2026-07-26T07:23:08.600971Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "* * * \n", "* * * \n", "* * * \n", "* * * \n" ] } ], "source": [ "# 目标：用两层 for 循环输出 3 行、每行 3 个星号。\n", "for row in range(4):\n", " for col in range(3):\n", " print(\"*\", end=\" \")\n", " print()\n", "\n" ] }, { "cell_type": "markdown", "id": "89427e52", "metadata": {}, "source": [ "## 9. break 与 continue：一个结束循环，一个跳过本轮\n", "\n", "- break：立即结束当前这一层循环。\n", "- continue：跳过当前轮余下代码，直接进入下一轮。" ] }, { "cell_type": "markdown", "id": "5f2e1d85", "metadata": {}, "source": [ "### 课堂演示（样本代码）\n", "\n", "先由教师运行下方样本代码，观察条件、循环变量和输出如何变化。" ] }, { "cell_type": "code", "execution_count": 36, "id": "ee1ef626", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.602941Z", "iopub.status.busy": "2026-07-26T07:23:08.602805Z", "iopub.status.idle": "2026-07-26T07:23:08.605429Z", "shell.execute_reply": "2026-07-26T07:23:08.605017Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "\n", "continue：\n", "P y t h n " ] } ], "source": [ "# print(\"break：\")\n", "# for letter in \"Python\":\n", "# if letter == \"o\":\n", "# break\n", "# print(letter, end=\" \")\n", "\n", "print(\"\\ncontinue：\")\n", "for letter in \"Python\":\n", " if letter == \"o\":\n", " continue\n", " print(letter, end=\" \")" ] }, { "cell_type": "markdown", "id": "b8eb27b5", "metadata": {}, "source": [ "### 课堂练习（学生填写）\n", "\n", "根据刚才的样本代码独立补全下方空位；完成后再运行并检查结果。" ] }, { "cell_type": "code", "execution_count": 18, "id": "bc1bc913", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.607559Z", "iopub.status.busy": "2026-07-26T07:23:08.607386Z", "iopub.status.idle": "2026-07-26T07:23:08.609194Z", "shell.execute_reply": "2026-07-26T07:23:08.608937Z" } }, "outputs": [], "source": [ "# 目标：遍历 Python，遇到 o 时跳过本轮，输出其他字符。\n", "# for letter in \"Python\":\n", "# if letter == \"o\":\n", "# # 请填写 continue\n", "# print(letter, end=\" \")" ] }, { "cell_type": "markdown", "id": "fa0fe5f1", "metadata": {}, "source": [ "## 10. 实训一：会员等级评定\n", "\n", "同时满足消费金额和积分门槛才升级。规则从高到低判断，避免低等级先被命中。" ] }, { "cell_type": "markdown", "id": "fb17b486", "metadata": {}, "source": [ "### 课堂演示（样本代码）\n", "\n", "先由教师运行下方样本代码，观察条件、循环变量和输出如何变化。" ] }, { "cell_type": "code", "execution_count": 19, "id": "12e6d03f", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.610807Z", "iopub.status.busy": "2026-07-26T07:23:08.610673Z", "iopub.status.idle": "2026-07-26T07:23:08.613501Z", "shell.execute_reply": "2026-07-26T07:23:08.613145Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "消费 600、积分 5200： 白金会员\n", "消费 250、积分 100： 普通会员\n", "消费 100、积分 500： 非会员\n" ] } ], "source": [ "def member_level(amount, points):\n", " if amount >= 500 and points >= 5000:\n", " return \"白金会员\"\n", " if amount >= 200 or points >= 2000:\n", " return \"普通会员\"\n", " return \"非会员\"\n", "\n", "\n", "print(\"消费 600、积分 5200：\", member_level(600, 5200))\n", "print(\"消费 250、积分 100：\", member_level(250, 100))\n", "print(\"消费 100、积分 500：\", member_level(100, 500))" ] }, { "cell_type": "markdown", "id": "82206759", "metadata": {}, "source": [ "### 课堂练习（学生填写）\n", "\n", "根据刚才的样本代码独立补全下方空位；完成后再运行并检查结果。" ] }, { "cell_type": "code", "execution_count": 20, "id": "2b6fc05c", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.615733Z", "iopub.status.busy": "2026-07-26T07:23:08.615567Z", "iopub.status.idle": "2026-07-26T07:23:08.617436Z", "shell.execute_reply": "2026-07-26T07:23:08.617123Z" } }, "outputs": [], "source": [ "# 目标：补全白金和普通会员的判断。\n", "# def member_level(amount, points):\n", "# if amount >= 500 and points >= 5000:\n", "# return \"白金会员\"\n", "# return # 请填写\n", "#\n", "# print(member_level(600, 5200))" ] }, { "cell_type": "markdown", "id": "5686a282", "metadata": {}, "source": [ "## 11. 实训二：物流费用计算\n", "\n", "先验证地区和重量，再确定首重价与续重价。为练习条件分支，本例直接用 if-elif 判断三个地区，\n", "不使用字典查表。超过 2 kg 的部分按完整或不足 1 kg 都计为 1 kg。\n", "\n", "int(小数) 用于取小数的整数部分，例如 int(1.8) 的结果是 1。这里先取超出重量的整数部分，\n", "再用条件判断是否还需要加 1 kg。" ] }, { "cell_type": "markdown", "id": "3d57d90f", "metadata": {}, "source": [ "### 课堂演示（样本代码）\n", "\n", "先由教师运行下方样本代码，观察条件、循环变量和输出如何变化。" ] }, { "cell_type": "code", "execution_count": 21, "id": "dc554dbe", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.619071Z", "iopub.status.busy": "2026-07-26T07:23:08.618916Z", "iopub.status.idle": "2026-07-26T07:23:08.622313Z", "shell.execute_reply": "2026-07-26T07:23:08.621925Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "01，1.5 kg -> 13 元\n", "02，2 kg -> 12 元\n", "03，3.2 kg -> 22 元\n" ] } ], "source": [ "def shipping_fee(region_code, weight_kg):\n", " if weight_kg <= 0:\n", " return \"重量必须大于 0\"\n", "\n", " if region_code == \"01\":\n", " first_price, extra_price = 13, 3\n", " elif region_code == \"02\":\n", " first_price, extra_price = 12, 2\n", " elif region_code == \"03\":\n", " first_price, extra_price = 14, 4\n", " else:\n", " return \"地区编号只能是 01、02 或 03\"\n", "\n", " if weight_kg <= 2:\n", " return first_price\n", "\n", " extra_kg = int(weight_kg - 2)\n", " if weight_kg - 2 > extra_kg:\n", " extra_kg += 1\n", " return first_price + extra_kg * extra_price\n", "\n", "\n", "print(\"01，1.5 kg ->\", shipping_fee(\"01\", 1.5), \"元\")\n", "print(\"02，2 kg ->\", shipping_fee(\"02\", 2), \"元\")\n", "print(\"03，3.2 kg ->\", shipping_fee(\"03\", 3.2), \"元\")" ] }, { "cell_type": "markdown", "id": "f129a9da", "metadata": {}, "source": [ "### 课堂练习（学生填写）\n", "\n", "根据刚才的样本代码独立补全下方空位；完成后再运行并检查结果。" ] }, { "cell_type": "code", "execution_count": 22, "id": "3beab648", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.624308Z", "iopub.status.busy": "2026-07-26T07:23:08.624167Z", "iopub.status.idle": "2026-07-26T07:23:08.626066Z", "shell.execute_reply": "2026-07-26T07:23:08.625759Z" } }, "outputs": [], "source": [ "# 目标：华东地区首重 13 元、续重每 kg 3 元。补全 3.2 kg 的费用。\n", "# weight_kg = 3.2\n", "# first_price = 13\n", "# extra_price = 3\n", "# extra_kg = 2\n", "# fee = # 请填写\n", "# print(fee)" ] }, { "cell_type": "markdown", "id": "7b15b85a", "metadata": {}, "source": [ "## 12. 实训三：限制三次的登录检测\n", "\n", "循环次数明确时可用 for range(3)。成功后立即结束；三次都失败才给出锁定提示。\n", "\n", "本例的 attempts 中每一项都由用户名和密码组成。for user, password in attempts\n", "表示每次循环把这一项中的两个值分别放进 user 和 password。" ] }, { "cell_type": "markdown", "id": "6a837d11", "metadata": {}, "source": [ "### 课堂演示（样本代码）\n", "\n", "先由教师运行下方样本代码，观察条件、循环变量和输出如何变化。" ] }, { "cell_type": "code", "execution_count": 23, "id": "10b414ff", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.627572Z", "iopub.status.busy": "2026-07-26T07:23:08.627476Z", "iopub.status.idle": "2026-07-26T07:23:08.630864Z", "shell.execute_reply": "2026-07-26T07:23:08.630506Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "第 1 次：用户名或密码错误，还剩 2 次\n", "第 2 次：用户名或密码错误，还剩 1 次\n", "第 3 次：登录成功\n" ] } ], "source": [ "def login_check(attempts):\n", " expected_user = \"admin\"\n", " expected_password = \"python\"\n", " attempt_no = 0\n", "\n", " for user, password in attempts:\n", " attempt_no += 1\n", " if user == expected_user and password == expected_password:\n", " return f\"第 {attempt_no} 次：登录成功\"\n", "\n", " remaining = 3 - attempt_no\n", " if remaining > 0:\n", " print(f\"第 {attempt_no} 次：用户名或密码错误，还剩 {remaining} 次\")\n", "\n", " return \"输入错误次数过多，请稍后再试\"\n", "\n", "\n", "attempts = [(\"admin\", \"123\"), (\"guest\", \"python\"), (\"admin\", \"python\")]\n", "print(login_check(attempts))" ] }, { "cell_type": "markdown", "id": "25fdd12c", "metadata": {}, "source": [ "### 课堂练习（学生填写）\n", "\n", "根据刚才的样本代码独立补全下方空位；完成后再运行并检查结果。" ] }, { "cell_type": "code", "execution_count": 24, "id": "29a7c75f", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.633014Z", "iopub.status.busy": "2026-07-26T07:23:08.632857Z", "iopub.status.idle": "2026-07-26T07:23:08.634686Z", "shell.execute_reply": "2026-07-26T07:23:08.634411Z" } }, "outputs": [], "source": [ "# 目标：补全三次机会的核心判断；成功时立即结束。\n", "# attempts = [(\"admin\", \"123\"), (\"admin\", \"python\")]\n", "# attempt_no = 0\n", "# for user, password in attempts:\n", "# attempt_no += 1\n", "# if user == \"admin\" and password == \"python\":\n", "# # 请填写成功提示和结束循环\n", "# #" ] }, { "cell_type": "markdown", "id": "4b53c795", "metadata": {}, "source": [ "## 13. 拓展：按条件选择房贷年利率\n", "\n", "教材阶段案例的完整月供公式较长。课堂只练习其中最重要的流程控制部分：\n", "根据贷款类型和期限，用条件分支选择年利率。完整公式作为课后拓展阅读。" ] }, { "cell_type": "markdown", "id": "fecb9090", "metadata": {}, "source": [ "### 课堂演示（样本代码）\n", "\n", "先由教师运行下方样本代码，观察条件、循环变量和输出如何变化。" ] }, { "cell_type": "code", "execution_count": 25, "id": "fc97f979", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.636416Z", "iopub.status.busy": "2026-07-26T07:23:08.636273Z", "iopub.status.idle": "2026-07-26T07:23:08.639100Z", "shell.execute_reply": "2026-07-26T07:23:08.638710Z" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "商业贷款 3 年： 0.0475\n", "公积金贷款 10 年： 0.031\n" ] } ], "source": [ "def annual_rate(loan_type, years):\n", " if loan_type == \"商业\":\n", " if years <= 5:\n", " return 0.0475\n", " return 0.0490\n", " elif loan_type == \"公积金\":\n", " if years <= 5:\n", " return 0.0260\n", " return 0.0310\n", " return \"贷款类型只能是商业或公积金\"\n", "\n", "\n", "print(\"商业贷款 3 年：\", annual_rate(\"商业\", 3))\n", "print(\"公积金贷款 10 年：\", annual_rate(\"公积金\", 10))" ] }, { "cell_type": "markdown", "id": "b04ae0bf", "metadata": {}, "source": [ "### 课堂练习（学生填写）\n", "\n", "根据刚才的样本代码独立补全下方空位；完成后再运行并检查结果。" ] }, { "cell_type": "code", "execution_count": 26, "id": "f923fe96", "metadata": { "execution": { "iopub.execute_input": "2026-07-26T07:23:08.641298Z", "iopub.status.busy": "2026-07-26T07:23:08.641132Z", "iopub.status.idle": "2026-07-26T07:23:08.643041Z", "shell.execute_reply": "2026-07-26T07:23:08.642770Z" } }, "outputs": [], "source": [ "# 目标：补全公积金贷款的利率判断。\n", "# loan_type = \"公积金\"\n", "# years = 10\n", "# if loan_type == \"公积金\":\n", "# if years <= 5:\n", "# rate = # 请填写\n", "# else:\n", "# rate = # 请填写\n", "# print(rate)" ] }, { "cell_type": "markdown", "id": "e7d02d8b", "metadata": {}, "source": [ "## 14. 离场检验\n", "\n", "- 多分支为什么应先判断高阈值？\n", "- range(2, 6) 会产生哪些数？\n", "- break 和 continue 分别改变什么？\n", "- 写循环前，能否说清初值、条件、更新？" ] } ], "metadata": { "kernelspec": { "display_name": "vix", "language": "python", "name": "python3" }, "language_info": { "codemirror_mode": { "name": "ipython", "version": 3 }, "file_extension": ".py", "mimetype": "text/x-python", "name": "python", "nbconvert_exporter": "python", "pygments_lexer": "ipython3", "version": "3.11.8" }, "updated_for": "每个知识点采用课堂演示与学生留空练习，移除未讲解的复杂用法" }, "nbformat": 4, "nbformat_minor": 5 }