为什么序列是mypy中+不支持的操作数类型？

Question

[mypy给出的错误是Sequence[str]运算符不支持+：]]

# test.py

from typing import Sequence


def test(x: Sequence[str], y: Sequence[str]) -> Sequence[str]:
    return x + y

$ mypy test.py
test.py:5: error: Unsupported left operand type for + ("Sequence[str]")
Found 1 error in 1 file (checked 1 source file)
pytype给出了类似的错误：

$ pytype test.py 

[...]

  No attribute '__add__' on Sequence[str] or '__radd__' on Sequence[str]

[...]
为什么Sequence[str]是+不受支持的操作数类型？

mypy给出了一个错误，表明+运算符不支持Sequence [str]类型的操作数：＃test.py来自输入import序列def test（x：Sequence [str]，y：Sequence [str]）->序列[str]：...

Answer 1

根据文档，序列不一定实现__add__：