if语句用于根据条件决定是否执行特定的代码块。
# 基本if语句
age = 18
if age >= 18:
print("成年人")
print("可以投票")
# if-else语句
score = 85
if score >= 60:
print("及格")
else:
print("不及格")
# if-elif-else语句
grade = 85
if grade >= 90:
print("优秀")
elif grade >= 80:
print("良好")
elif grade >= 70:
print("中等")
elif grade >= 60:
print("及格")
else:
print("不及格")# 多重条件判断
age = 25
income = 50000
credit_score = 750
# 使用逻辑运算符组合条件
if age >= 18 and income >= 30000 and credit_score >= 700:
print("符合贷款条件")
elif age >= 18 and income >= 50000:
print("部分符合条件，需要提高信用分数")
else:
print("不符合贷款条件")
# 嵌套if语句
username = "admin"
password = "123456"
is_active = True
if username == "admin":
if password == "123456":
if is_active:
print("登录成功")
else:
print("账户已被禁用")
else:
print("密码错误")
else:
print("用户名不存在")
# 使用in运算符
fruits = ["apple", "banana", "orange"]
fruit = "apple"
if fruit in fruits:
print(f"{fruit}在水果列表中")
else:
print(f"{fruit}不在水果列表中")match语句是Python 3.10引入的新特性，提供了一种更优雅的方式来处理多个条件分支。
# 基本match语句
def analyze_command(command):
match command:
case "start":
return "启动系统"
case "stop":
return "停止系统"
case "restart":
return "重启系统"
case _: # 默认情况
return "未知命令"
# 测试match语句
print(analyze_command("start")) # 启动系统
print(analyze_command("unknown")) # 未知命令
# 带值的模式匹配
def analyze_status(status):
match status:
case 200:
return "成功"
case 404:
return "未找到"
case 500:
return "服务器错误"
case code if 100 <= code < 200:
return "信息响应"
case code if 300 <= code < 400:
return "重定向"
case code if 400 <= code < 500:
return "客户端错误"
case code if 500 <= code < 600:
return "服务器错误"
case _:
return "未知状态码"
# 测试状态码分析
print(analyze_status(200)) # 成功
print(analyze_status(404)) # 未找到
print(analyze_status(301)) # 重定向# 解构模式匹配
def analyze_point(point):
match point:
case (0, 0):
return "原点"
case (0, y):
return f"Y轴上的点，y={y}"
case (x, 0):
return f"X轴上的点，x={x}"
case (x, y):
return f"普通点({x}, {y})"
case _:
return "无效点"
# 测试点分析
print(analyze_point((0, 0))) # 原点
print(analyze_point((0, 5))) # Y轴上的点，y=5
print(analyze_point((3, 0))) # X轴上的点，x=3
print(analyze_point((2, 3))) # 普通点(2, 3)
# 列表模式匹配
def analyze_list(lst):
match lst:
case []:
return "空列表"
case [x]:
return f"单元素列表: {x}"
case [x, y]:
return f"双元素列表: {x}, {y}"
case [x, y, z]:
return f"三元素列表: {x}, {y}, {z}"
case [first, *rest]:
return f"多元素列表，首元素: {first}，其余: {rest}"
case _:
return "无效列表"
# 测试列表分析
print(analyze_list([])) # 空列表
print(analyze_list([1])) # 单元素列表: 1
print(analyze_list([1, 2])) # 双元素列表: 1, 2
print(analyze_list([1, 2, 3, 4])) # 多元素列表，首元素: 1，其余: [2, 3, 4]
# 字典模式匹配
def analyze_config(config):
match config:
case {"type": "user", "name": name, "age": age}:
return f"用户配置: {name}, {age}岁"
case {"type": "admin", "name": name, "permissions": perms}:
return f"管理员配置: {name}, 权限: {perms}"
case {"type": "guest"}:
return "访客配置"
case {"type": type_name, **rest}:
return f"其他类型配置: {type_name}, 其他参数: {rest}"
case _:
return "无效配置"
# 测试配置分析
print(analyze_config({"type": "user", "name": "Alice", "age": 25}))
print(analyze_config({"type": "admin", "name": "Bob", "permissions": ["read", "write"]}))
print(analyze_config({"type": "guest"}))# 游戏状态管理
def handle_game_command(command, player_state):
match command:
case ["move", direction]:
return f"玩家向{direction}方向移动"
case ["attack", target]:
return f"玩家攻击{target}"
case ["use", item, target]:
return f"玩家使用{item}在{target}上"
case ["inventory"]:
return "显示背包"
case ["quit"]:
return "退出游戏"
case _:
return "未知命令"
# 测试游戏命令
print(handle_game_command(["move", "north"], {}))
print(handle_game_command(["attack", "goblin"], {}))
print(handle_game_command(["use", "potion", "self"], {}))
# HTTP请求处理
def handle_http_request(method, path, headers):
match (method, path):
case ("GET", "/"):
return {"status": 200, "content": "首页"}
case ("GET", "/users" | "/users/"):
return {"status": 200, "content": "用户列表"}
case ("GET", f"/users/{user_id}"):
return {"status": 200, "content": f"用户{user_id}信息"}
case ("POST", "/users"):
return {"status": 201, "content": "用户创建成功"}
case ("PUT", f"/users/{user_id}"):
return {"status": 200, "content": f"用户{user_id}更新成功"}
case ("DELETE", f"/users/{user_id}"):
return {"status": 204, "content": f"用户{user_id}删除成功"}
case _:
return {"status": 404, "content": "页面未找到"}
# 测试HTTP请求处理
print(handle_http_request("GET", "/", {}))
print(handle_http_request("GET", "/users/123", {}))
print(handle_http_request("POST", "/users", {}))
# 数据类型分析
def analyze_data(data):
match data:
case None:
return "空值"
case bool():
return f"布尔值: {data}"
case int():
return f"整数: {data}"
case float():
return f"浮点数: {data}"
case str():
return f"字符串: {data}"
case list():
return f"列表，长度: {len(data)}"
case dict():
return f"字典，键数: {len(data)}"
case _:
return f"其他类型: {type(data).__name__}"
# 测试数据类型分析
print(analyze_data(None))
print(analyze_data(42))
print(analyze_data("Hello"))
print(analyze_data([1, 2, 3]))
print(analyze_data({"a": 1, "b": 2}))# 使用if-elif-else的传统方式
def analyze_command_traditional(command):
if command == "start":
return "启动系统"
elif command == "stop":
return "停止系统"
elif command == "restart":
return "重启系统"
else:
return "未知命令"
# 使用match的现代方式
def analyze_command_modern(command):
match command:
case "start":
return "启动系统"
case "stop":
return "停止系统"
case "restart":
return "重启系统"
case _:
return "未知命令"
# 复杂条件对比
def analyze_user_traditional(user):
if isinstance(user, dict):
if user.get("type") == "admin":
if user.get("permissions"):
return f"管理员，权限: {user['permissions']}"
else:
return "管理员，无特殊权限"
elif user.get("type") == "user":
return f"普通用户: {user.get('name', 'Unknown')}"
else:
return "未知用户类型"
else:
return "无效用户数据"
def analyze_user_modern(user):
match user:
case {"type": "admin", "permissions": perms}:
return f"管理员，权限: {perms}"
case {"type": "admin"}:
return "管理员，无特殊权限"
case {"type": "user", "name": name}:
return f"普通用户: {name}"
case {"type": "user"}:
return "普通用户: Unknown"
case _:
return "无效用户数据"
# 测试对比
user1 = {"type": "admin", "permissions": ["read", "write"]}
user2 = {"type": "user", "name": "Alice"}
print(analyze_user_traditional(user1))
print(analyze_user_modern(user1))
print(analyze_user_traditional(user2))
print(analyze_user_modern(user2))# 遍历列表
fruits = ["apple", "banana", "orange"]
for fruit in fruits:
print(f"我喜欢{fruit}")
# 遍历字符串
for char in "Python":
print(char)
# 使用range()函数
for i in range(5):
print(i) # 0, 1, 2, 3, 4
for i in range(1, 6):
print(i) # 1, 2, 3, 4, 5
for i in range(0, 10, 2):
print(i) # 0, 2, 4, 6, 8
# 遍历字典
person = {"name": "Alice", "age": 25, "city": "Beijing"}
for key in person:
print(f"{key}: {person[key]}")
for key, value in person.items():
print(f"{key}: {value}")
# 使用enumerate()获取索引
fruits = ["apple", "banana", "orange"]
for index, fruit in enumerate(fruits):
print(f"{index}: {fruit}")# 基本while循环
count = 0
while count < 5:
print(f"计数: {count}")
count += 1
# 用户输入循环
password = "secret"
attempts = 0
max_attempts = 3
while attempts < max_attempts:
user_input = input("请输入密码: ")
if user_input == password:
print("登录成功！")
break
else:
attempts += 1
print(f"密码错误，还剩{max_attempts - attempts}次机会")
# 无限循环与break
while True:
user_input = input("请输入命令 (quit退出): ")
if user_input.lower() == "quit":
break
print(f"执行命令: {user_input}")
# 使用continue跳过当前迭代
for i in range(10):
if i % 2 == 0:
continue # 跳过偶数
print(i) # 只打印奇数# break语句 - 提前结束循环
for i in range(10):
if i == 5:
break
print(i) # 只打印0到4
# continue语句 - 跳过当前迭代
for i in range(10):
if i == 5:
continue
print(i) # 打印0-4, 6-9，跳过5
# else子句 - 循环正常结束时执行
for i in range(5):
print(i)
else:
print("循环正常结束")
# break时不会执行else
for i in range(5):
if i == 3:
break
print(i)
else:
print("这行不会执行")
# 实际应用：查找元素
numbers = [1, 3, 5, 7, 9]
search_value = 4
for num in numbers:
if num == search_value:
print(f"找到{search_value}")
break
else:
print(f"未找到{search_value}")# 嵌套if语句
age = 25
income = 50000
credit_score = 750
if age >= 18:
if income >= 30000:
if credit_score >= 700:
print("完全符合贷款条件")
elif credit_score >= 600:
print("需要提高信用分数")
else:
print("信用分数过低")
else:
print("收入不足")
else:
print("年龄不符合要求")
# 多层嵌套的实际应用
def check_eligibility(age, income, credit_score, employment_years):
if age >= 18:
if income >= 30000:
if credit_score >= 700:
if employment_years >= 2:
return "完全符合条件"
else:
return "工作年限不足"
elif credit_score >= 600:
return "信用分数需要提高"
else:
return "信用分数过低"
else:
return "收入不足"
else:
return "年龄不符合要求"
# 测试函数
result = check_eligibility(25, 50000, 750, 3)
print(result)# 打印乘法表
for i in range(1, 10):
for j in range(1, i + 1):
print(f"{j}×{i}={i*j}", end="\t")
print() # 换行
# 二维数组遍历
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
for row in matrix:
for element in row:
print(element, end=" ")
print()
# 查找二维数组中的元素
def find_element(matrix, target):
for i, row in enumerate(matrix):
for j, element in enumerate(row):
if element == target:
return (i, j)
return None
# 测试查找函数
result = find_element(matrix, 5)
print(f"元素5的位置: {result}")
# 嵌套循环中的break和continue
for i in range(3):
for j in range(3):
if i == 1 and j == 1:
break # 只跳出内层循环
print(f"({i}, {j})")
print("内层循环结束")# 1. 使用早期返回减少嵌套
def check_loan_eligibility(age, income, credit_score):
if age < 18:
return "年龄不符合要求"
if income < 30000:
return "收入不足"
if credit_score < 700:
return "信用分数过低"
return "符合贷款条件"
# 2. 使用列表推导式替代简单循环
# 传统方式
squares = []
for i in range(10):
if i % 2 == 0:
squares.append(i ** 2)
# 列表推导式
squares = [i ** 2 for i in range(10) if i % 2 == 0]
# 3. 使用any()和all()函数
numbers = [2, 4, 6, 8, 10]
all_even = all(num % 2 == 0 for num in numbers)
any_odd = any(num % 2 == 1 for num in numbers)
# 4. 使用enumerate()获取索引
fruits = ["apple", "banana", "orange"]
for index, fruit in enumerate(fruits, 1):
print(f"{index}. {fruit}")
# 5. 使用zip()同时遍历多个列表
names = ["Alice", "Bob", "Charlie"]
ages = [25, 30, 35]
cities = ["Beijing", "Shanghai", "Guangzhou"]
for name, age, city in zip(names, ages, cities):
print(f"{name} is {age} years old and lives in {city}")# 1. 可变默认参数陷阱
def add_item(item, items=[]): # 错误：可变默认参数
items.append(item)
return items
# 正确做法
def add_item(item, items=None):
if items is None:
items = []
items.append(item)
return items
# 2. 循环中修改列表
numbers = [1, 2, 3, 4, 5]
# 错误做法
for i in range(len(numbers)):
if numbers[i] % 2 == 0:
numbers.remove(numbers[i]) # 会跳过元素
# 正确做法
numbers = [num for num in numbers if num % 2 != 0]
# 3. 浮点数比较
# 错误做法
if 0.1 + 0.2 == 0.3:
print("相等")
# 正确做法
if abs(0.1 + 0.2 - 0.3) < 1e-10:
print("相等")
# 4. 无限循环
# 错误做法
i = 0
while i < 10:
print(i)
# 忘记增加i
# 正确做法
i = 0
while i < 10:
print(i)
i += 1# 学生成绩管理系统
students = [
{"name": "Alice", "scores": [85, 90, 78, 92]},
{"name": "Bob", "scores": [72, 68, 85, 79]},
{"name": "Charlie", "scores": [95, 88, 92, 96]},
{"name": "Diana", "scores": [65, 70, 68, 72]}
]
def calculate_average(scores):
return sum(scores) / len(scores)
def get_grade(average):
if average >= 90:
return "A"
elif average >= 80:
return "B"
elif average >= 70:
return "C"
elif average >= 60:
return "D"
else:
return "F"
def analyze_students():
print("学生成绩分析报告")
print("=" * 40)
for student in students:
name = student["name"]
scores = student["scores"]
average = calculate_average(scores)
grade = get_grade(average)
print(f"学生: {name}")
print(f"成绩: {scores}")
print(f"平均分: {average:.2f}")
print(f"等级: {grade}")
# 分析各科成绩
for i, score in enumerate(scores, 1):
if score >= 90:
print(f" 科目{i}: 优秀")
elif score >= 80:
print(f" 科目{i}: 良好")
elif score >= 70:
print(f" 科目{i}: 中等")
elif score >= 60:
print(f" 科目{i}: 及格")
else:
print(f" 科目{i}: 不及格")
print("-" * 40)
# 运行分析
analyze_students()import random
def guess_number_game():
# 生成1-100的随机数
target = random.randint(1, 100)
attempts = 0
max_attempts = 10
print("欢迎来到猜数字游戏！")
print(f"我已经想好了一个1-100之间的数字，你有{max_attempts}次机会猜测。")
while attempts < max_attempts:
try:
guess = int(input(f"第{attempts + 1}次猜测，请输入数字: "))
attempts += 1
if guess < 1 or guess > 100:
print("请输入1-100之间的数字！")
continue
if guess == target:
print(f"恭喜！你用了{attempts}次就猜对了！")
break
elif guess < target:
print("太小了，再大一点！")
else:
print("太大了，再小一点！")
# 提示剩余次数
remaining = max_attempts - attempts
if remaining > 0:
print(f"还有{remaining}次机会")
except ValueError:
print("请输入有效的数字！")
continue
else:
print(f"游戏结束！正确答案是{target}")
# 运行游戏
if __name__ == "__main__":
guess_number_game()