python/day03/variables_operators_basics.py

"""variables_operators_basics.py - Python 变量与运算符基础示例

涵盖：变量定义、命名规则、赋值、类型推断、常见算术运算符、比较运算符、
逻辑运算符、赋值运算符、成员运算符、身份运算符，以及运算优先级说明。
"""


def main():
    # 1. 变量：用来存储数据的标识符
    name = "Alice"
    age = 18
    height = 1.72
    is_student = True

    print("name ->", name)
    print("age ->", age)
    print("height ->", height)
    print("is_student ->", is_student)

    # 2. 变量命名规则
    # - 只能包含字母、数字、下划线
    # - 不能以数字开头
    # - 不能使用 Python 关键字
    # - 建议使用 snake_case
    user_name = "Bob"
    max_score = 100
    print("user_name ->", user_name)
    print("max_score ->", max_score)

    # 3. 多变量赋值
    a, b, c = 10, 20, 30
    print("a, b, c ->", a, b, c)

    x = y = 100
    print("x == y ->", x == y)

    # 4. 动态类型：变量不需要声明类型，赋值时自动决定类型
    num = 10
    num = "ten"
    print("num after reassignment ->", num)

    # 5. 算术运算符
    print("5 + 3 ->", 5 + 3)
    print("5 - 3 ->", 5 - 3)
    print("5 * 3 ->", 5 * 3)
    print("10 / 3 ->", 10 / 3)      # 浮点除法
    print("10 // 3 ->", 10 // 3)    # 整除
    print("10 % 3 ->", 10 % 3)      # 取余
    print("2 ** 3 ->", 2 ** 3)      # 幂运算

    # 6. 比较运算符
    print("5 > 3 ->", 5 > 3)
    print("5 == 3 ->", 5 == 3)
    print("5 != 3 ->", 5 != 3)
    print("5 >= 3 ->", 5 >= 3)
    print("5 <= 3 ->", 5 <= 3)

    # 7. 逻辑运算符
    print("True and False ->", True and False)
    print("True or False ->", True or False)
    print("not True ->", not True)

    # 8. 赋值运算符
    total = 10
    total += 5    # total = total + 5
    total *= 2    # total = total * 2
    print("total ->", total)

    # 9. 身份运算符：判断两个对象是否为同一个对象
    p = [1, 2]
    q = p
    r = [1, 2]
    print("p is q ->", p is q)
    print("p is r ->", p is r)

    # 10. 成员运算符：判断元素是否在序列里
    fruits = ["apple", "banana", "orange"]
    print("'apple' in fruits ->", 'apple' in fruits)
    print("'pear' not in fruits ->", 'pear' not in fruits)

    # 11. 位运算符（进阶，了解即可）
    print("5 & 3 ->", 5 & 3)
    print("5 | 3 ->", 5 | 3)
    print("5 ^ 3 ->", 5 ^ 3)
    print("~5 ->", ~5)

    # 12. 运算优先级（从高到低）
    # 一般顺序：括号 > 幂运算 > 乘除取模 > 加减 > 比较 > not > and > or
    result = 10 + 3 * 2 ** 2
    print("10 + 3 * 2 ** 2 ->", result)

    # 13. 变量的作用
    # - 存储数据
    # - 程序中用于表达、计算、判断
    # - 让代码更清晰、可维护

    # 14. 小结
    # Python 中变量没有固定类型，运算符用于进行计算、比较、逻辑判断和赋值。
    # 根据需要选择合适的运算符即可。


# if __name__ == '__main__':
#     main()


p = [1, 2]
q = p
r = [1, 2]
print("p is q ->", p is q)
print("p is r ->", p is r)
print("p == r ->", p == r)