2.13.运算符

a = 10
b = 3

print(a + b)   # 13
print(a - b)   # 7
print(a * b)   # 30
print(a / b)   # 3.333...
print(a // b)  # 3
print(a % b)   # 1
print(a ** b)  # 1000

x = 10
y = 5

print(x == y)   # False
print(x != y)   # True
print(x > y)    # True
print(x < y)    # False
print(x >= 10)  # True
print(y <= 3)   # False

a = True
b = False

print(a and b)  # False
print(a or b)   # True
print(not a)    # False
print(not b)    # True

# 实际应用
age = 25
has_license = True

if age >= 18 and has_license:
    print("可以开车")
else:
    print("不能开车")

# = 简单赋值
x = 10
print(x)  # 10

# += 加法赋值
x += 5    # 相当于 x = x + 5
print(x)  # 15

# -= 减法赋值
x -= 3    # 相当于 x = x - 3
print(x)  # 12

# *= 乘法赋值
x *= 2    # 相当于 x = x * 2
print(x)  # 24

# /= 除法赋值
x /= 4    # 相当于 x = x / 4
print(x)  # 6.0

# //= 整除赋值
x //= 3   # 相当于 x = x // 3
print(x)  # 2.0

# %= 取模赋值
x %= 2    # 相当于 x = x % 2
print(x)  # 0.0

# **= 幂赋值
x = 3
x **= 3   # 相当于 x = x ** 3
print(x)  # 27

# 位运算符示例
a = 10    # 二进制: 1010
b = 4     # 二进制: 0100

print(a & b)   # 0  (1000 & 0100 = 0000)
print(a | b)   # 14 (1010 | 0100 = 1110)
print(a ^ b)   # 14 (1010 ^ 0100 = 1110)
print(~a)      # -11  x的取反等于-x-1
print(a << 1)  # 20 (1010 << 1 = 10100)
print(a >> 1)  # 5  (1010 >> 1 = 0101)

# 身份运算符示例
a = [1, 2, 3]
b = a
c = [1, 2, 3]

print(a is b)      # True (同一个对象)
print(a is c)      # False (值相同但不是同一个对象)
print(a == c)      # True (值相等)

print(a is not c)  # True

# 成员运算符示例
fruits = ["苹果", "香蕉", "橙子"]

print("苹果" in fruits)      # True
print("葡萄" in fruits)      # False
print("香蕉" not in fruits)  # False
print("西瓜" not in fruits)  # True

# 字符串中的成员运算
text = "Hello, World!"
print("Hello" in text)       # True
print("Python" in text)      # False

# 优先级示例
result1 = 2 + 3 * 4      # 3*4先计算，然后+2 = 14
result2 = (2 + 3) * 4    # 括号优先，5*4 = 20
result3 = 10 - 4 + 2     # 从左到右，6+2 = 8
result4 = 2 ** 3 * 4     # 2**3先计算，8*4 = 32
result5 = 15 / 3 * 2     # 从左到右，5*2 = 10.0

print(result1)  # 14
print(result2)  # 20
print(result3)  # 8
print(result4)  # 32
print(result5)  # 10.0

# 复杂表达式
a = 5
b = 3
c = 2

result = a + b * c ** 2  # 2**2=4, 3*4=12, 5+12=17
print(result)  # 17

# 使用括号明确优先级
result_clear = a + (b * (c ** 2))
print(result_clear)  # 17

# 结合性示例
# 从左到右
result1 = 10 - 3 - 2    # (10-3)=7, 7-2=5
print(result1)  # 5

# 从右到左
result2 = 2 ** 3 ** 2   # 3**2=9, 2**9=512
print(result2)  # 512

# 赋值运算符从右到左
a = b = c = 10
print(a, b, c)  # 10 10 10

 a=b=c=d=e=1
 # 难以理解
 result = a + b * c - d / e
 print(result)
 # 更清晰
 result = a + (b * c) - (d / e)
 print(result)

 a=b=c=d=e=f=g=1
 # 过于复杂
 result = (a + b) * (c - d) / (e ** f) % g
 print(result)
 # 分解为多个步骤
 temp1 = a + b
 temp2 = c - d
 temp3 = e ** f
 result = (temp1 * temp2) / temp3 % g
 print(result)

# 整数除法
print(5 / 2)   # 2.5 (浮点数)
print(5 // 2)  # 2 (整数)

# 字符串运算
print("Hello" + "World")  # "HelloWorld"
print("Hi" * 3)           # "HiHiHi"

v1 = "zhangsan" and "lisi"

# 分析过程：
# 步骤1：判断 "zhangsan" 的真假 → 非空字符串为 True
# 步骤2：因为前面是 True，继续判断后面
# 步骤3：返回后面的值

print(v1)  # "lisi"

v2 = "" and "lisi"

# 分析过程：
# 步骤1：判断 "" 的真假 → 空字符串为 False
# 步骤2：因为前面是 False，短路求值，不再判断后面
# 步骤3：返回前面的值

print(v2)  # ""

# 数字示例
print(1 and 2)        # 2  - 1为真，返回2
print(0 and 100)      # 0  - 0为假，返回0
print(5 and 0)        # 0  - 5为真，继续判断，返回0

# 列表示例
print([1, 2] and [3, 4])  # [3, 4] - 非空列表为真，返回后面
print([] and [1, 2])      # []     - 空列表为假，返回前面

# 混合类型
print("hello" and 0)      # 0      - 字符串为真，返回0
print(None and "world")   # None   - None为假，返回None

# 多个 and 连接
print("a" and "b" and "c")  # "c"   - 都为真，返回最后一个
print(1 and 0 and 3)        # 0     - 遇到0停止，返回0
print(1 and 2 and "")       # ""    - 遇到空字符串停止

v3 = 1 or 8

# 分析过程：
# 步骤1：判断 1 的真假 → 非零数字为 True
# 步骤2：因为前面是 True，短路求值，不再判断后面
# 步骤3：返回前面的值

print(v3)  # 1

v4 = 0 or 8

# 分析过程：
# 步骤1：判断 0 的真假 → 0为 False
# 步骤2：因为前面是 False，继续判断后面
# 步骤3：返回后面的值

print(v4)  # 8

# 数字示例
print(0 or 5)         # 5     - 0为假，返回5
print(3 or 10)        # 3     - 3为真，返回3
print(0 or 0 or 1)    # 1     - 前两个为假，返回1

# 字符串示例
print("" or "hello")      # "hello" - 空字符串为假，返回"hello"
print("hi" or "bye")      # "hi"    - "hi"为真，返回"hi"
print("" or "" or "ok")   # "ok"    - 前两个为假，返回"ok"

# 列表示例
print([] or [1, 2])       # [1, 2]  - 空列表为假，返回[1, 2]
print([5] or [10])        # [5]     - [5]为真，返回[5]

# 混合类型
print(None or "default")  # "default" - None为假，返回"default"
print(False or 0 or "")   # ""        - 都为假，返回最后一个

# 使用 or 提供默认值
username = input("请输入用户名：") or "匿名用户"
print(f"欢迎，{username}！")

# 如果用户输入为空，使用默认值
name = "" or "Guest"
print(name)  # "Guest"

# 配置项默认值
config = {}
port = config.get("port") or 8080
print(port)  # 8080

# 根据条件选择值
is_vip = True
discount = is_vip and 0.8 or 1.0
print(f"折扣：{discount}")  # 0.8

# 等价于
if is_vip:
    discount = 0.8
else:
    discount = 1.0

import os
config = {}
# 获取第一个有效值
result = None or "" or 0 or "找到了" or "backup"
print(result)  # "找到了"
# 从多个来源获取配置
db_host = os.getenv("DB_HOST") or config.get("db_host") or "localhost"

# 只有满足条件才执行
debug_mode = True
debug_mode and print("调试信息：正在运行...")

# 等价于
if debug_mode:
    print("调试信息：正在运行...")

# 复杂的逻辑运算
result1 = "a" and "b" or "c"
print(result1)  # "b"
# 解析：("a" and "b") → "b"，然后 "b" or "c" → "b"

result2 = "" and "b" or "c"
print(result2)  # "c"
# 解析：("" and "b") → ""，然后 "" or "c" → "c"

result3 = 0 or [] or {} or "default"
print(result3)  # "default"
# 解析：所有都为假值，返回最后一个

result4 = [1] or [2] and [3]
print(result4)  # [1]
# 解析：[1]为真，短路求值，直接返回[1]
# 注意：and 优先级高于 or

print(bool(None))        # False
print(bool(0))           # False
print(bool(""))          # False
print(bool([]))          # False
print(bool({}))          # False

print(bool("hello"))     # True
print(bool([1, 2]))      # True
print(bool(1))           # True
print(bool(-1))          # True

result = True or False and False
# 等价于 True or (False and False)
print(result)  # True

def func():
    print("函数被调用了")
    return True

# 因为短路求值，func() 不会被调用
result = True or func()
# 输出：无

# func() 会被调用
result = False or func()
# 输出：函数被调用了

 a = True
 b = False
 c = True
 d = False
 e = "e"
 # 不推荐：难以理解
 value = a and b or c and d or e
 # 推荐：使用 if-else 更清晰
 if a and b:
     value = b
 elif c and d:
     value = d
 else:
     value = e