Python中的Walrus运算符分析示例详解

data = [1, 2, 3, 4, 5]
while len(data) > 0:
    print(data.pop())

data = [1, 2, 3, 4, 5]
while (n := len(data)) > 0:
    print(data.pop())

# 读取文件直到遇到空行
with open("file.txt", "r") as f:
    line = f.readline()
    while line.strip() != "":
        print(line)
        line = f.readline()

with open("file.txt", "r") as f:
    while (line := f.readline().strip()) != "":
        print(line)

# 计算平方数，并过滤出偶数的平方
squares = [x*x for x in range(10) if (square := x*x) % 2 == 0]
print(squares)  # 输出：[0, 4, 16, 36, 64]

# 根据条件赋值并返回结果
value = 10
result = (x := value) if x > 5 else (x := 0)
print(result)  # 输出：10
print(x)       # 输出：10

def get_data():
    return {"a": 1, "b": 2}
# 传统写法
data = get_data()
if data["a"] > 0:
    print(f"a: {data['a']}, b: {data['b']}")
# 使用Walrus运算符
if (data := get_data())["a"] > 0:
    print(f"a: {data['a']}, b: {data['b']}")

# 计算并记录中间结果
result = (x := 2 + 3) * (y := 4 + 5)
print(f"x={x}, y={y}, result={result}")  # 输出：x=5, y=9, result=45

# 不推荐：
a := 10  # 错误！Walrus必须在表达式中使用，不能单独使用

a = 10