typing_literal.md

2019.06.17 22:00+09:00

python3.8にmypyをインストール。まだmasterじゃないとインストールできない。

$ git clone --recurse-submodules https://github.com/python/mypy.git
$ cd mypy
$ python3.8 setup.py install

だがしかし、python3.8は from typing import Literal で、 mypyはまだ from typing_extensions import Literal でないとimportできない。

python実行

literaltypes1.py

from typing import Literal

def spam(mode: Literal["egg", "hum"]):
    print(mode)

if __name__ == '__main__':
    spam("salad")

$ python3.8 literaltypes1.py
salad

mypyでチェック

literaltypes2.py

from typing_extensions import Literal

def spam(mode: Literal["egg", "hum"]):
    print(mode)

if __name__ == '__main__':
    spam("salad")

$ mypy literaltypes2.py
literaltypes2.py:7: error: Argument 1 to "spam" has incompatible type "Literal['salad']"; expected "Union[Literal['egg'], Literal['hum']]"