海象运算符python 3.8支持

1.实现赋值

EXPERIMENTAL = 123

if c_o := EXPERIMENTAL:
    print(c_o)
    
# 结果：
# 123

2. 避免len()方法运行两次，提高了运行速度.

a = (1, 2, 3, 4, 5)
if (n := len(a)) > 3:
    print(f"List is too long ({n} elements, expected <= 10)")