第3章：控制结构与函数定义
📚 学习目标
Specific (具体)：
- 掌握Python中的条件控制语句（if/elif/else）
- 熟练使用循环结构（for/while）解决重复性任务
- 理解函数的定义、调用和参数传递机制
- 掌握变量作用域和函数设计原则
Measurable (可衡量)：
- 能够编写至少20个不同的控制结构代码示例
- 正确完成95%以上的条件和循环练习题
- 独立设计并实现包含多个函数的完整程序
Achievable (可实现)：
- 通过循序渐进的理论学习和实践练习
- 从简单条件判断到复杂程序控制逻辑
Relevant (相关性)：
- 为算法设计和程序架构打下基础
- 培养结构化编程思维
Time-bound (时限性)：
- 2周内完成本章学习（4课时理论+实践）
🗺️ 知识导图
💡 3.1 条件控制结构
3.1.1 if语句基础
条件控制是程序根据不同情况做出不同决策的机制。Python使用if语句实现条件控制。
# 基本if语句age = 18if age >= 18:print("你已经成年了")print("可以申请身份证")# if-else双分支score = 85if score >= 60:print("恭喜你，考试通过了！")else:print("很遗憾，需要重考")# 多分支elifgrade = 92if grade >= 90:level = "优秀"elif grade >= 80:level = "良好"elif grade >= 70:level = "中等"elif grade >= 60:level = "及格"else:level = "不及格"print(f"你的成绩等级是：{level}")
3.1.2 复杂条件判断
# 逻辑运算符组合条件age = 25income = 8000credit_score = 750# 贷款审批条件if age >= 18 and age <= 65 and income >= 5000 and credit_score >= 700:print("贷款申请通过")else:print("贷款申请不符合条件")# 使用in关键字user_role = "admin"if user_role in ["admin", "manager", "supervisor"]:print("有管理权限")else:print("普通用户权限")# 条件表达式（三元操作符）temperature = 25weather = "舒适" if 15 <= temperature <= 30 else "不适宜"print(f"今天天气{weather}")
3.1.3 嵌套条件和实用技巧
def evaluate_student(score, attendance):""" 学生综合评价系统"""if score >= 0 and score <= 100: # 分数有效性检查if attendance >= 80: # 出勤率检查if score >= 90:return "优秀学生"elif score >= 80:return "良好学生"elif score >= 60:return "合格学生"else:return "需要补习"else:return "出勤率不足，无法评级"else:return "分数输入错误"# 测试函数print(evaluate_student(95, 90)) # 优秀学生print(evaluate_student(75, 70)) # 出勤率不足，无法评级
🔄 3.2 循环控制结构
3.2.1 for循环详解
for循环用于遍历序列（字符串、列表 、元组等）或其他可迭代对象。
# 基本for循环fruits = ["苹果", "香蕉", "橙子", "葡萄"]for fruit in fruits:print(f"我喜欢吃{fruit}")# 使用range()函数print("倒计时：")for i in range(10, 0, -1):print(i)print("发射！")# enumerate()获取索引和值students = ["小明", "小红", "小强"]for index, name in enumerate(students, 1):print(f"第{index}名学生：{name}")# zip()同时遍历多个序列names = ["张三", "李四", "王五"]scores = [95, 87, 92]subjects = ["数学", "英语", "物理"]for name, score, subject in zip(names, scores, subjects):print(f"{name}的{subject}成绩是{score}分")
3.2.2 while循环应用
while循环在条件为真时重复执行代码块。
# 基本while循环count = 1while count <= 5:print(f"这是第{count}次循环")count += 1# 用户输入验证while True:password = input("请输入密码：")if len(password) >= 8:print("密码设置成功！")breakelse:print("密码长度至少8位，请重新输入")# 数字猜谜游戏import randomsecret_number = random.randint(1, 100)attempts = 0max_attempts = 7print("我想了一个1到100之间的数字，你能猜到吗？")print(f"你有{max_attempts}次机会")while attempts < max_attempts:try:guess = int(input("请输入你的猜测："))attempts += 1if guess == secret_number:print(f"恭喜你！猜对了！答案是{secret_number}")print(f"你用了{attempts}次机会")breakelif guess < secret_number:print("太小了，再试试")else:print("太大了，再试试")print(f"剩余机会：{max_attempts - attempts}")except ValueError:print("请输入有效数字")attempts -= 1 # 无效输入不计入次数if attempts >= max_attempts:print(f"游戏结束！答案是{secret_number}")
3.2.3 循环控制语句
# break和continue的使用print("找出1-20中的所有质数：")for num in range(2, 21):is_prime = Truefor i in range(2, int(num ** 0.5) + 1):if num % i == 0:is_prime = Falsebreak # 找到因数，跳出内层循环if is_prime:print(num, end=" ")print("\n")# continue跳过当前迭代print("1-10中的奇数：")for i in range(1, 11):if i % 2 == 0:continue # 跳过偶数print(i, end=" ")print("\n")# for-else结构def find_item(items, target):"""在列表中查找元素"""for item in items:if item == target:print(f"找到了{target}")breakelse:print(f"没有找到{target}")shopping_list = ["苹果", "面包", "牛奶"]find_item(shopping_list, "面包") # 找到了面包find_item(shopping_list, "鸡蛋") # 没有找到鸡蛋### 3.2.4 实际应用场景#### Web开发中的循环应用
# 处理用户表单数据def process_form_data(form_data):"""处理Web表单数据"""processed_data = {}required_fields = ['username', 'email', 'password']# 验证必填字段for field in required_fields:if field not in form_data or not form_data[field].strip():return {'error': f'字段 {field} 是必填的'}processed_data[field] = form_data[field].strip()# 处理可选字段optional_fields = ['phone', 'address', 'bio']for field in optional_fields:if field in form_data:processed_data[field] = form_data[field].strip()return {'success': True, 'data': processed_data}# 模拟表单数据sample_form = {'username': 'john_doe','email': 'john@example.com','password': 'secure123','phone': '123-456-7890'}result = process_form_data(sample_form)print(result)# 批量处理API响应def process_api_responses(responses):"""批量处理API响应数据"""successful_responses = []failed_responses = []for i, response in enumerate(responses):try:if response['status'] == 'success':successful_responses.append({'index': i,'data': response['data']})else:failed_responses.append({'index': i,'error': response.get('error', 'Unknown error')})except KeyError as e:failed_responses.append({'index': i,'error': f'Invalid response format: {e}'})return {'successful': successful_responses,'failed': failed_responses,'total': len(responses)}# 模拟API响应api_responses = [{'status': 'success', 'data': {'id': 1, 'name': 'Item 1'}},{'status': 'error', 'error': 'Not found'},{'status': 'success', 'data': {'id': 3, 'name': 'Item 3'}},{'invalid': 'response'}]results = process_api_responses(api_responses)print(f"成功处理: {len(results['successful'])} 个")print(f"失败处理: {len(results['failed'])} 个")
数据处理中的循环优化
# 高效的数据过滤和转换def process_data_efficiently(data_list, filters=None, transformations=None):"""高效处理数据列表"""if filters is None:filters = []if transformations is None:transformations = []processed_data = []for item in data_list:# 应用过滤器should_include = Truefor filter_func in filters:if not filter_func(item):should_include = Falsebreakif not should_include:continue# 应用转换processed_item = item.copy() if isinstance(item, dict) else itemfor transform_func in transformations:processed_item = transform_func(processed_item)processed_data.append(processed_item)return processed_data# 使用示例sample_data = [{'id': 1, 'name': 'Alice', 'age': 25, 'salary': 50000},{'id': 2, 'name': 'Bob', 'age': 30, 'salary': 60000},{'id': 3, 'name': 'Charlie', 'age': 22, 'salary': 45000},{'id': 4, 'name': 'Diana', 'age': 35, 'salary': 75000}]# 定义过滤器和转换器age_filter = lambda x: x['age'] >= 25salary_filter = lambda x: x['salary'] >= 50000name_upper = lambda x: {**x, 'name': x['name'].upper()}add_bonus = lambda x: {**x, 'bonus': x['salary'] * 0.1}# 应用处理result = process_data_efficiently(sample_data,filters=[age_filter, salary_filter],transformations=[name_upper, add_bonus])print("处理结果:")for item in result:print(f" {item['name']}: 年龄{item['age']}, 薪资{item['salary']}, 奖金{item['bonus']}")
## 🔧 3.3 函数设计与实现
### 3.3.1 函数定义基础
函数是可重用的代码块，用于执行特定任务。
<CodeExecutor executable language="python">
{`# 基本函数定义
\ndef greet():
\n \"\"\"简单的问候函数\"\"\"
\n print(\"Hello, World!\")
\n
\n# 调用函数
\ngreet()
\n
\n# 带参数的函数
\ndef greet_person(name):
\n \"\"\"个性化问候函数\"\"\"
\n print(f\"Hello, {name}!\")
\n
\ngreet_person(\"小明\")
\n
\n# 带返回值的函数
\ndef add_numbers(a, b):
\n \"\"\"计算两个数的和\"\"\"
\n result = a + b
\n return result
\n
\nsum_result = add_numbers(10, 20)
\nprint(f\"10 + 20 = {sum_result}\")
\n
\n# 带默认参数的函数
\ndef introduce(name, age=18, city=\"北京\"):
\n \"\"\"自我介绍函数\"\"\"
\n return f\"我叫{name}，今年{age}岁，来自{city}\"
\n
\nprint(introduce(\"小红\"))
\nprint(introduce(\"小明\", 25))
\nprint(introduce(\"小李\", 30, \"上海\"))`}
</CodeExecutor>
### 3.3.2 参数传递机制
<CodeExecutor executable language="python">
{`# 位置参数和关键字参数
\ndef create_profile(name, age, city, hobby):
\n \"\"\"创建用户档案\"\"\"
\n return {
\n \"姓名\": name,
\n \"年龄\": age,
\n \"城市\": city,
\n \"爱好\": hobby
\n }
\n
\n# 位置参数调用
\nprofile1 = create_profile(\"张三\", 25, \"北京\", \"读书\")
\n
\n# 关键字参数调用
\nprofile2 = create_profile(
\n hobby=\"游泳\",
\n name=\"李四\",
\n city=\"上海\",
\n age=28
\n)
\n
\n# 混合调用（位置参数 必须在关键字参数前面）
\nprofile3 = create_profile(\"王五\", 22, city=\"广州\", hobby=\"音乐\")
\n
\nprint(profile1)
\nprint(profile2)
\n
\n# 可变参数 *args
\ndef calculate_sum(*numbers):
\n \"\"\"计算任意数量数字的和\"\"\"
\n total = 0
\n for num in numbers:
\n total += num
\n return total
\n
\nprint(calculate_sum(1, 2, 3))
\nprint(calculate_sum(10, 20, 30, 40, 50))
\n
\n# 关键字可 变参数 **kwargs
\ndef create_student(**info):
\n \"\"\"创建学生信息\"\"\"
\n student = {}
\n for key, value in info.items():
\n student[key] = value
\n return student
\n
\nstudent1 = create_student(name=\"小明\", age=20, major=\"计算机\")
\nstudent2 = create_student(name=\"小红\", grade=3, school=\"清华大学\", gpa=3.8)
\n
\nprint(student1)
\nprint(student2)`}
</CodeExecutor>
### 3.3.3 变量作用域
<CodeExecutor executable language="python">
{`# 全局变量和局部变量
\nglobal_var = \"我是全局变量\"
\n
\ndef scope_demo():
\n local_var = \"我是局部变量\"
\n print(f\"函数内部访问全局变量：{global_var}\")
\n print(f\"函数内部访问局部变量：{local_var}\")
\n
\nscope_demo()
\nprint(f\"函数外部访问全局变量：{global_var}\")
\n# print(local_var) # 这会报错，局部变量在函数外不可访问
\n
\n# 使用global关键字修改全局变量
\ncounter = 0
\n
\ndef increment():
\n global counter
\n counter += 1
\n print(f\"计数器值：{counter}\")
\n
\nincrement() # 计数器值：1
\nincrement() # 计数器值：2
\n
\n# 函数嵌套和nonlocal
\ndef outer_function():
\n outer_var = \"外层函数变量\"
\n
\n def inner_function():
\n nonlocal outer_var
\n outer_var = \"被内层函数修改的变量\"
\n print(f\"内层函数：{outer_var}\")
\n
\n print(f\"修改前：{outer_var}\")
\n inner_function()
\n print(f\"修改后：{outer_var}\")
\n
\nouter_function()`}
</CodeExecutor>
### 3.3.4 递归函数
<CodeExecutor executable language="python">
{`# 计算阶乘
\ndef factorial(n):
\n \"\"\"计算n的阶乘\"\"\"
\n if n <= 1:
\n return 1
\n else:
\n return n * factorial(n - 1)
\n
\nprint(f\"5! = {factorial(5)}\") # 5! = 120
\n
\n# 斐波那契数列
\ndef fibonacci(n):
\n \"\"\"计算斐波那契数列第n项\"\"\"
\n if n <= 1:
\n return n
\n else:
\n return fibonacci(n - 1) + fibonacci(n - 2)
\n
\n# 打印前10项斐波那契数列
\nprint(\"斐波那契数列前10项：\")
\nfor i in range(10):
\n print(fibonacci(i), end=\" \")
\nprint()
\n
\n# 汉诺塔问题
\ndef hanoi(n, source, target, auxiliary):
\n \"\"\"解决汉诺塔问题\"\"\"
\n if n == 1:
\n print(f\"将盘子从{source}移动到{target}\")
\n else:
\n hanoi(n - 1, source, auxiliary, target)
\n print(f\"将盘子从{source}移动到{target}\")
\n hanoi(n - 1, auxiliary, target, source)
\n
\nprint(\"解决3层汉诺塔问题：\")
\nhanoi(3, \"A\", \"C\", \"B\")
\n
\n### 3.5.2 生成器函数
\n
\n生成器函数使用\`yield\`关键字，可以逐个产生值而不一次性生成所有数据。`}
</CodeExecutor>
<CodeExecutor executable language="python">
{`# 基本生成器函数
\ndef fibonacci_generator(n):
\n \"\"\"生成斐波那契数列的前n个数\"\"\"
\n a, b = 0, 1
\n count = 0
\n while count < n:
\n yield a
\n a, b = b, a + b
\n count += 1
\n
\n# 使用生成器
\nprint(\"斐波那契数列前10个数：\")
\nfor num in fibonacci_generator(10):
\n print(num, end=\" \")
\nprint()
\n
\n# 内存高效的生成器
\ndef read_large_file(file_path):
\n \"\"\"逐行读取大文件，避免内存溢出\"\"\"
\n with open(file_path, \'r\', encoding=\'utf-8\') as file:
\n for line in file:
\n yield line.strip()
\n
\n# 模拟大文件处理
\ndef process_data_stream():
\n \"\"\"处理数据流的生成器\"\"\"
\n data = [\"数据1\", \"数据2\", \"数据3\", \"数据4\", \"数据5\"]
\n for item in data:
\n # 模拟处理时间
\n yield f\"已处理: {item}\"
\n
\n# 使用生成器处理数据
\nfor processed_item in process_data_stream():
\n print(processed_item)`}
</CodeExecutor>
### 3.5.3 闭包和装饰器
#### 闭包函数
<CodeExecutor executable language="python">
{`# 闭包：函数返回另一个函数
\ndef create_counter():
\n \"\"\"创建计数器闭包\"\"\"
\n count = 0
\n
\n def counter():
\n nonlocal count
\n count += 1
\n return count
\n
\n return counter
\n
\n# 使用闭包
\ncounter1 = create_counter()
\ncounter2 = create_counter()
\n
\nprint(f\"计数器1: {counter1()}\") # 1
\nprint(f\"计数器1: {counter1()}\") # 2
\nprint(f\"计数器2: {counter2()}\") # 1
\nprint(f\"计数器1: {counter1()}\") # 3
\n
\n# 带参数的闭包
\ndef create_multiplier(factor):
\n \"\"\"创建乘法器闭包\"\"\"
\n def multiplier(x):
\n return x * factor
\n return multiplier
\n
\ndouble = create_multiplier(2)
\ntriple = create_multiplier(3)
\n
\nprint(f\"2的2倍: {double(2)}\") # 4
\nprint(f\"3的3倍: {triple(3)}\") # 9`}
</CodeExecutor>
#### 装饰器基础
<CodeExecutor executable language="python">
{`# 基本装饰器
\ndef timer_decorator(func):
\n \"\"\"计时装饰器\"\"\"
\n import time
\n
\n def wrapper(*args, **kwargs):
\n start_time = time.time()
\n result = func(*args, **kwargs)
\n end_time = time.time()
\n print(f\"{func.__name__} 执行时间: {end_time - start_time:.4f}秒\")
\n return result
\n
\n return wrapper
\n
\n# 使用装饰器
\n@timer_decorator
\ndef slow_function():
\n \"\"\"模拟耗时函数\"\"\"
\n import time
\n time.sleep(1)
\n return \"完成\"
\n
\n# 调用被装饰的函数
\nresult = slow_function()
\n
\n# 带参数的装饰器
\ndef retry_decorator(max_attempts=3):
\n \"\"\"重试装饰器\"\"\"
\n def decorator(func):
\n def wrapper(*args, **kwargs):
\n for attempt in range(max_attempts):
\n try:
\n return func(*args, **kwargs)
\n except Exception as e:
\n if attempt == max_attempts - 1:
\n raise e
\n print(f\"第{attempt + 1}次尝试失败，重试中...\")
\n return None
\n return wrapper
\n return decorator
\n
\n# 使用带参数的装饰器
\n@retry_decorator(max_attempts=3)
\ndef unreliable_function():
\n \"\"\"模拟不稳定的函数\"\"\"
\n import random
\n if random.random() < 0.7: # 70%概率失败
\n raise Exception(\"随机错误\")
\n return \"成功\"
\n
\n# 测试重试机制
\ntry:
\n result = unreliable_function()
\n print(f\"最终结果: {result}\")
\nexcept Exception as e:
\n print(f\"所有重试都失败了: {e}\")`}
</CodeExecutor>
### 3.5.4 函数式编程工具
<CodeExecutor executable language="python">
{`# 高阶函数：map, filter, reduce
\nfrom functools import reduce
\n
\n# map函数：对序列中的每个元素应用函数
\nnumbers = [1, 2, 3, 4, 5]
\nsquared = list(map(lambda x: x**2, numbers))
\nprint(f\"平方数: {squared}\") # [1, 4, 9, 16, 25]
\n
\n# filter函数：过滤序列中的元素
\neven_numbers = list(filter(lambda x: x % 2 == 0, numbers))
\nprint(f\"偶数: {even_numbers}\") # [2, 4]
\n
\n# reduce函数：累积计算
\nsum_all = reduce(lambda x, y: x + y, numbers)
\nprint(f\"总和: {sum_all}\") # 15
\n
\n# 函数组合
\ndef compose(*functions):
\n \"\"\"函数组合器\"\"\"
\n def inner(arg):
\n for f in reversed(functions):
\n arg = f(arg)
\n return arg
\n return inner
\n
\n# 使用函数组合
\nadd_one = lambda x: x + 1
\nmultiply_by_two = lambda x: x * 2
\nsquare = lambda x: x ** 2
\n
\ncombined = compose(square, multiply_by_two, add_one)
\nresult = combined(3) # ((3 + 1) * 2) ^ 2 = 64
\nprint(f\"组合函数结果: {result}\")
\n
\n# 偏函数：固定部分参数
\nfrom functools import partial
\n
\ndef power(base, exponent):
\n \"\"\"计算幂\"\"\"
\n return base ** exponent
\n
\n# 创建平方函数
\nsquare_func = partial(power, exponent=2)
\ncube_func = partial(power, exponent=3)
\n
\nprint(f\"5的平方: {square_func(5)}\") # 25
\nprint(f\"3的立方: {cube_func(3)}\") # 27`}
</CodeExecutor>
🔬 代码示例集合
示例1：智能成绩管理系统
def grade_management_system():"""智能成绩管理系统"""students = {}def add_student(name, scores):"""添加学生成绩"""students[name] = scoresprint(f"已添加学生：{name}")def calculate_average(scores):"""计算平均分"""return sum(scores) / len(scores) if scores else 0def get_grade_level(average):"""根据平均分获取等级"""if average >= 90:return "优秀"elif average >= 80:return "良好"elif average >= 70:return "中等"elif average >= 60:return "及格"else:return "不及格"def display_report():"""显示成绩报告"""print("\n=== 成绩报告 ===")print(f"{'姓名':<10} {'平均分':<10} {'等级':<10}")print("-" * 35)for name, scores in students.items():avg = calculate_average(scores)level = get_grade_level(avg)print(f"{name:<10} {avg:<10.1f} {level:<10}")# 添加示例数据add_student("张三", [85, 92, 78, 88])add_student("李四", [76, 81, 79, 85])add_student("王五", [95, 98, 93, 97])display_report()# 运行系统grade_management_system()
示例2：菜单驱动的计算器
def advanced_calculator():"""菜单驱动的高级计算器"""def show_menu():"""显示菜单"""print("\n=== 高级计算器 ===")print("1. 基本运算")print("2. 科学计算")print("3. 统计计算")print("4. 查看历史")print("5. 退出")print("=" * 20)def basic_operations():"""基本运算"""while True:print("\n基本运算：+、-、*、/")expression = input("请输入表达式（如：10 + 5），输入q返回主菜单：")if expression.lower() == 'q':breaktry:result = eval(expression)print(f"结果：{expression} = {result}")history.append(f"{expression} = {result}")except:print("表达式错误，请重新输入")def scientific_operations():"""科学计算"""import mathfunctions = {'1': ('平方根', lambda x: math.sqrt(x)),'2': ('平方', lambda x: x ** 2),'3': ('立方', lambda x: x ** 3),'4': ('对数', lambda x: math.log(x)),'5': ('正弦', lambda x: math.sin(math.radians(x))),'6': ('余弦', lambda x: math.cos(math.radians(x)))}while True:print("\n科学计算功能：")for key, (name, _) in functions.items():print(f"{key}. {name}")print("0. 返回主菜单")choice = input("请选择功能：")if choice == '0':breakif choice in functions:try:x = float(input("请输入数值："))name, func = functions[choice]result = func(x)print(f"{name}({x}) = {result}")history.append(f"{name}({x}) = {result}")except Exception as e:print(f"计算错误：{e}")else:print("无效选择")def statistics_operations():"""统计计算"""while True:print("\n统计计算")numbers_input = input("请输入数字列表（用空格分隔），输入q返回：")if numbers_input.lower() == 'q':breaktry:numbers = [float(x) for x in numbers_input.split()]if numbers:mean = sum(numbers) / len(numbers)max_num = max(numbers)min_num = min(numbers)print(f"数据：{numbers}")print(f"平均值：{mean:.2f}")print(f"最大值：{max_num}")print(f"最小值：{min_num}")history.append(f"统计：{numbers} -> 平均:{mean:.2f}")else:print("请输入 有效数字")except ValueError:print("输入格式错误")def show_history():"""显示历史记录"""print("\n=== 计算历史 ===")if history:for i, record in enumerate(history[-10:], 1):print(f"{i}. {record}")else:print("暂无历史记录")# 主程序history = []while True:show_menu()choice = input("请选择功能：")if choice == '1':basic_operations()elif choice == '2':scientific_operations()elif choice == '3':statistics_operations()elif choice == '4':show_history()elif choice == '5':print("感谢使用计算器！")breakelse:print("无效选择，请重新输入")# 运行计算器（注释掉避免实际运行）# advanced_calculator()
🎯 实践练习
基础练习
练习1：年龄分类器
def age_classifier():"""根据年龄进行分类"""# 请完成以下功能：# 0-2岁：婴儿# 3-6岁：幼儿# 7-17岁：少年# 18-59岁：成年人# 60岁以上：老年人pass# 测试用例ages = [1, 5, 12, 25, 65]for age in ages:print(f"{age}岁：{age_classifier(age)}")
练习2：九九乘法表
def multiplication_table():"""生成九九乘法表"""# 请使用嵌套循环生成完整的九九乘法表# 格式：1×1=1 1×2=2 1×3=3...passmultiplication_table()
中级练习
练习3：密码强度检查器
def password_strength_checker(password):"""检查密码强度"""# 请实现以下检查规则：# 1. 长度至少8位# 2. 包含大写字母# 3. 包含小写字母# 4. 包含数字# 5. 包含特殊字符# 返回强度等级：弱、中、强pass# 测试用例passwords = ["123456", "abcdefgh", "Abc123456", "Abc@123456"]for pwd in passwords:strength = password_strength_checker(pwd)print(f"密码'{pwd}'强度：{strength}")
挑战练习
练习4：简单银行系统
class SimpleBankSystem:"""简单银行系统"""def __init__(self):self.accounts = {}self.next_account_id = 1001def create_account(self, name, initial_deposit=0):"""创建账户"""# 请实现账户创建功能passdef deposit(self, account_id, amount):"""存款"""# 请实现存款功能passdef withdraw(self, account_id, amount):"""取款"""# 请实现取款功能（需要检查余额）passdef transfer(self, from_account, to_account, amount):"""转账"""# 请实现转账功能passdef get_balance(self, account_id):"""查询余额"""# 请实现余额查询功能pass# 测试系统bank = SimpleBankSystem()# 请编写测试代码
🚀 项目案例：任务管理系统
import jsonimport datetimeclass TaskManager:"""任务管理系统"""def __init__(self):self.tasks = []self.next_id = 1self.load_tasks()def add_task(self, title, description="", priority="medium", due_date=None):"""添加任务"""task = {"id": self.next_id,"title": title,"description": description,"priority": priority,"due_date": due_date,"status": "pending","created_at": datetime.datetime.now().isoformat(),"completed_at": None}self.tasks.append(task)self.next_id += 1self.save_tasks()print(f"任务 '{title}' 添加成功，ID：{task['id']}")def list_tasks(self, status_filter=None):"""列出任务"""print("\n=== 任务列表 ===")filtered_tasks = self.tasksif status_filter:filtered_tasks = [t for t in self.tasks if t["status"] == status_filter]if not filtered_tasks:print("暂无任务")return# 按优先级排序priority_order = {"high": 1, "medium": 2, "low": 3}filtered_tasks.sort(key=lambda x: priority_order.get(x["priority"], 2))print(f"{'ID':<5} {'标题':<20} {'优先级':<8} {'状态':<10} {'截止日期':<12}")print("-" * 70)for task in filtered_tasks:due_date = task["due_date"] or "无"print(f"{task['id']:<5} {task['title']:<20} {task['priority']:<8} "f"{task['status']:<10} {due_date:<12}")def complete_task(self, task_id):"""完成任务"""for task in self.tasks:if task["id"] == task_id:task["status"] = "completed"task["completed_at"] = datetime.datetime.now().isoformat()self.save_tasks()print(f"任务 '{task['title']}' 已完成")returnprint(f"未找到ID为 {task_id} 的任务")def delete_task(self, task_id):"""删除任务"""for i, task in enumerate(self.tasks):if task["id"] == task_id:deleted_task = self.tasks.pop(i)self.save_tasks()print(f"任务 '{deleted_task['title']}' 已删除")returnprint(f"未找到ID为 {task_id} 的任务")def save_tasks(self):"""保存任务到文件"""try:with open("tasks.json", "w", encoding="utf-8") as f:json.dump(self.tasks, f, ensure_ascii=False, indent=2)except Exception as e:print(f"保存失败：{e}")def load_tasks(self):"""从文件加载任务"""try:with open("tasks.json", "r", encoding="utf-8") as f:self.tasks = json.load(f)if self.tasks:self.next_id = max(task["id"] for task in self.tasks) + 1except FileNotFoundError:print("任务文件不存在，创建新的任务列表")except Exception as e:print(f"加载失败：{e}")def search_tasks(self, keyword):"""搜索任务"""results = []keyword = keyword.lower()for task in self.tasks:if (keyword in task["title"].lower() orkeyword in task["description"].lower()):results.append(task)if results:print(f"\n找到 {len(results)} 个相关任务：")self._display_tasks(results)else:print(f"未找到包含 '{keyword}' 的任务")def get_statistics(self):"""获取任务统计信息"""total_tasks = len(self.tasks)completed_tasks = len([t for t in self.tasks if t["status"] == "completed"])pending_tasks = total_tasks - completed_tasks# 按优先级统计high_priority = len([t for t in self.tasks if t["priority"] == "high"])medium_priority = len([t for t in self.tasks if t["priority"] == "medium"])low_priority = len([t for t in self.tasks if t["priority"] == "low"])# 计算完成率completion_rate = (completed_tasks / total_tasks * 100) if total_tasks > 0 else 0print("\n=== 任务统计 ===")print(f"总任务数: {total_tasks}")print(f"已完成: {completed_tasks}")print(f"待完成: {pending_tasks}")print(f"完成率: {completion_rate:.1f}%")print(f"高优先级: {high_priority}")print(f"中优先级: {medium_priority}")print(f"低优先级: {low_priority}")def edit_task(self, task_id):"""编辑任务"""for task in self.tasks:if task["id"] == task_id:print(f"\n编辑任务: {task['title']}")print("留空表示不修改")new_title = input("新标题: ").strip()if new_title:task["title"] = new_titlenew_description = input("新描述: ").strip()if new_description:task["description"] = new_descriptionnew_priority = input("新优先级 (high/medium/low): ").strip()if new_priority in ["high", "medium", "low"]:task["priority"] = new_prioritynew_due_date = input("新截止日期 (YYYY-MM-DD): ").strip()if new_due_date:task["due_date"] = new_due_dateself.save_tasks()print("任务更新成功")returnprint(f"未找到ID为 {task_id} 的任务")def _display_tasks(self, tasks):"""显示任务列表（内部方法）"""if not tasks:print("暂无任 务")return# 按优先级排序priority_order = {"high": 1, "medium": 2, "low": 3}tasks.sort(key=lambda x: priority_order.get(x["priority"], 2))print(f"{'ID':<5} {'标题':<20} {'优先级':<8} {'状态':<10} {'截止日期':<12}")print("-" * 70)for task in tasks:due_date = task["due_date"] or "无"print(f"{task['id']:<5} {task['title']:<20} {task['priority']:<8} "f"{task['status']:<10} {due_date:<12}")def run(self):"""运行主程序"""while True:print("\n=== 任务管理系统 ===")print("1. 添加任务")print("2. 查看所有任务")print("3. 查看待完成任务")print("4. 查看已完成任务")print("5. 完成任务")print("6. 删除任务")print("7. 编辑任务")print("8. 搜索任务")print("9. 查看统计")print("10. 退出")choice = input("请选择操作：").strip()if choice == "1":title = input("任务标题：").strip()if title:description = input("任务描述（可选）：").strip()priority = input("优先级（high/medium/low，默认medium）：").strip() or "medium"due_date = input("截止日期（YYYY-MM-DD，可选）：").strip() or Noneself.add_task(title, description, priority, due_date)else:print("任务标题不能为空")elif choice == "2":self.list_tasks()elif choice == "3":self.list_tasks("pending")elif choice == "4":self.list_tasks("completed")elif choice == "5":try:task_id = int(input("请输入要完成的任务ID："))self.complete_task(task_id)except ValueError:print("请输入有效的任务ID")elif choice == "6":try:task_id = int(input("请输入要删除的任务ID："))confirm = input("确认删除？(y/N)：").lower()if confirm == "y":self.delete_task(task_id)except ValueError:print("请输入有效的任务ID")elif choice == "7":try:task_id = int(input("请输入要编辑的任务ID："))self.edit_task(task_id)except ValueError:print("请输入有效的任务ID")elif choice == "8":keyword = input("请输入搜索关键词：").strip()if keyword:self.search_tasks(keyword)else:print("搜索关键词不能为空")elif choice == "9":self.get_statistics()elif choice == "10":print("感谢使用任务管理系统！")breakelse:print("无效选择，请重新输入")# 演示程序（注释掉避免实际运行）def demo_task_manager():"""演示任务管理系统"""tm = TaskManager()# 添加示例任务tm.add_task("完成Python作业", "第3章练习题", "high", "2025-02-01")tm.add_task("准备考试", "数据结构考试复习", "high", "2025-02-05")tm.add_task("买菜", "周末去超市", "low")tm.add_task("学习机器学习", "深度学习基础课程", "medium", "2025-02-10")tm.add_task("健身", " 每周三次锻炼", "medium")# 显示任务列表tm.list_tasks()# 完成一个任务tm.complete_task(1)# 显示统计信息tm.get_statistics()# 搜索任务tm.search_tasks("学习")# 显示待完成任务tm.list_tasks("pending")# demo_task_manager()### 3.6.5 单元测试示例
import unittestclass TestTaskManager(unittest.TestCase):"""任务管理系统测试类"""def setUp(self):"""测试前的准备工作"""self.tm = TaskManager()# 清空任务列表self.tm.tasks = []self.tm.next_id = 1def test_add_task(self):"""测试添加任务功能"""self.tm.add_task("测试任务", "测试描述", "high")self.assertEqual(len(self.tm.tasks), 1)self.assertEqual(self.tm.tasks[0]["title"], "测试任务")self.assertEqual(self.tm.tasks[0]["priority"], "high")def test_complete_task(self):"""测试完成任务功能"""self.tm.add_task("测试任务")self.tm.complete_task(1)self.assertEqual(self.tm.tasks[0]["status"], "completed")def test_delete_task(self):"""测试删除任务功能"""self.tm.add_task("测试任务")initial_count = len(self.tm.tasks)self.tm.delete_task(1)self.assertEqual(len(self.tm.tasks), initial_count - 1)def test_search_tasks(self):"""测试搜索任务功能"""self.tm.add_task("Python学习", "学习Python编程")self.tm.add_task("Java学习", "学习Java编程")# 模拟搜索功能（这里需要修改search_tasks方法以返回结果）python_tasks = [t for t in self.tm.tasks if "Python" in t["title"]]self.assertEqual(len(python_tasks), 1)def test_task_statistics(self):"""测试任务统计功能"""self.tm.add_task("任务1", priority="high")self.tm.add_task("任务2", priority="medium")self.tm.add_task("任务3", priority="low")high_priority = len([t for t in self.tm.tasks if t["priority"] == "high"])self.assertEqual(high_priority, 1)# 运行测试if __name__ == "__main__":unittest.main()
3.6.6 性能优化示例
import timeimport cProfileimport pstatsdef performance_test():"""性能测试示例"""def slow_function():"""模拟慢函数"""time.sleep(0.1)return sum(range(1000))def fast_function():"""模拟快函数"""return sum(range(1000))# 使用cProfile进行性能分析profiler = cProfile.Profile()profiler.enable()# 执行慢函数for _ in range(10):slow_function()profiler.disable()# 输出性能统计stats = pstats.Stats(profiler)stats.sort_stats('cumulative')stats.print_stats(10)# performance_test()
## 📖 拓展阅读
### 在线资源
- [Python官方文档 - 控制流](https://docs.python.org/zh-cn/3/tutorial/controlflow.html)
- [Real Python - Python函数](https://realpython.com/defining-your-own-python-function/)
- [GeeksforGeeks - Python循环](https://www.geeksforgeeks.org/loops-in-python/)
### 推荐书籍
- 《Python编程快速上手》- Al Sweigart
- 《Python算法教程》- Magnus Lie Hetland
- 《编程珠玑》- Jon Bentley
---
## 📋 本章检查清单
** 理论掌握** ✅
- [ ] 掌握if/elif/else条件控制语句
- [ ] 熟练使用for和while循环
- [ ] 理解函数定义、调用和参数传递
- [ ] 掌握变量作用域和递归概念
- [ ] 理解生成器函数和闭包
- [ ] 掌握装饰器和函数式编程
**实践能力** ✅
- [ ] 能够编写复杂的条件判断逻辑
- [ ] 熟练使用循环解决重复性任务
- [ ] 能够设计和实现函数模块
- [ ] 独立完成综合性程序项目
- [ ] 掌握Web开发和数据处理应用
- [ ] 能够编写单元测试和性能优化
**项目经验** ✅
- [ ] 完成任务管理系统项目
- [ ] 理解程序的模块化设计
- [ ] 掌握数据持久化的基本方法
- [ ] 实现搜索和统计功能
- [ ] 掌握错误处理和用户交互
- [ ] 了解测试驱动开发方法
恭喜！你已经掌握了Python的控制结构和函数设计。下一章我们将学习面向对象编程。