# 合法的变量命名示例 counter = 10 user_name = "Alice" PI_VALUE = 3.14159 is_valid = True totalAmount = 100.50 # 不合法的变量命名示例 # 2nd_place = "Silver" # 不能以数字开头 # user-name = "Bob" # 不能包含连字符 # class = "Python" # 不能使用关键字

# 基本赋值 x = 10 message = "Hello, Python!" # 多重赋值 a, b, c = 5, 10, 15 # 链式赋值 x = y = z = 0 # 增量赋值 count = 5 count += 3 # 等同于 count = count + 3

# 整数 age = 25 print(type(age)) # <class 'int'> # 浮点数 price = 19.99 print(type(price)) # <class 'float'> # 字符串 name = "Alice" print(type(name)) # <class 'str'> # 布尔值 is_student = True print(type(is_student)) # <class 'bool'> # 列表 fruits = ["apple", "banana", "cherry"] print(type(fruits)) # <class 'list'> # 元组 coordinates = (10.5, 20.3) print(type(coordinates)) # <class 'tuple'> # 字典 person = {"name": "Bob", "age": 30} print(type(person)) # <class 'dict'>

# 常量定义示例 PI = 3.1415926535 MAX_CONNECTIONS = 100 DEFAULT_TIMEOUT = 30 API_KEY = "a1b2c3d4e5"

# 方法1：使用枚举 from enum import Enum class Constants(Enum): PI = 3.14159 GRAVITY = 9.8 # 访问常量 print(Constants.PI.value) # 3.14159 # 方法2：使用属性装饰器创建只读属性 class Config: @property def MAX_USERS(self): return 100 config = Config() print(config.MAX_USERS) # 100 # config.MAX_USERS = 200 # 会引发AttributeError

# 全局变量 global_var = "I'm global" def function1(): # 局部变量 local_var = "I'm local" print(global_var) # 可以访问全局变量 print(local_var) # 可以访问局部变量 def function2(): # 修改全局变量需要声明 global global_var global_var = "Modified global" # 尝试访问function1的局部变量会出错 # print(local_var) # NameError: name 'local_var' is not defined function1() function2() print(global_var) # 输出: Modified global

# 定义常量 TAX_RATE = 0.08 DISCOUNT_THRESHOLD = 100 DISCOUNT_RATE = 0.1 # 定义变量 items = [ {"name": "Book", "price": 25.50}, {"name": "Pen", "price": 3.75}, {"name": "Notebook", "price": 12.99} ] # 计算小计 subtotal = sum(item["price"] for item in items) # 应用折扣 if subtotal > DISCOUNT_THRESHOLD: discount = subtotal * DISCOUNT_RATE else: discount = 0 # 计算税费和总计 taxable_amount = subtotal - discount tax = taxable_amount * TAX_RATE total = taxable_amount + tax # 打印结果 print(f"Subtotal: ${subtotal:.2f}") print(f"Discount: -${discount:.2f}") print(f"Tax ({TAX_RATE*100:.0f}%): ${tax:.2f}") print(f"Total: ${total:.2f}")

# 常量定义 MIN_PASSWORD_LENGTH = 8 MAX_USERNAME_LENGTH = 20 ALLOWED_SPECIAL_CHARS = "!@#$%^&*" def validate_registration(username, password, email): # 验证用户名 if len(username) < 3 or len(username) > MAX_USERNAME_LENGTH: return False, "用户名长度必须在3-20个字符之间" # 验证密码强度 if len(password) < MIN_PASSWORD_LENGTH: return False, "密码长度至少8个字符" has_upper = any(char.isupper() for char in password) has_lower = any(char.islower() for char in password) has_digit = any(char.isdigit() for char in password) has_special = any(char in ALLOWED_SPECIAL_CHARS for char in password) if not (has_upper and has_lower and has_digit and has_special): return False, "密码必须包含大小写字母、数字和特殊字符" # 简单验证电子邮件 if "@" not in email or "." not in email: return False, "无效的电子邮件地址" return True, "注册信息有效" # 测试验证函数 result, message = validate_registration("alice2023", "SecurePass123!", "alice@example.com") print(f"验证结果: {result}, 消息: {message}")