带结构类型的Pathlib的Python类型提示（PEP 544）

Question

我有一个项目，其中PosixPath（pathlib）的类型提示将非常有用。我认为这应该是可行的，使用类似这样的结构类型-

# Python 3.8.5
from typing import Protocol
from pathlib import Path, PosixPath

class SupportsPosixPath(Protocol):
    def obj(self) -> PosixPath:
         ...

_home: SupportsPosixPath = Path("~")
_application_dir: SupportsPosixPath = Path("application")
_data_dir: SupportsPosixPath = Path("data")

def do_path_stuff(_home, _application_dir, _data_dir) -> SupportsPosixPath:
     _complete_path = _home.joinpath(_application_dir)
     _complete_path = _complete_path.joinpath(_data_dir)
     _complete_path = _complete_path.expanduser()
     _complete_path = (
     _complete_path.ascii_lowercase()
     )  # This should raise a linter error because PosixPath doesn't support ascii_lowercase.
     return _complete_path

PyCharm linter不会引发任何错误/问题。当我对^^^^运行mypy时，我得到-

$ mypy foo.py 
foo.py:11: error: Incompatible types in assignment (expression has type "Path", variable has type "SupportsPosixPath")
foo.py:12: error: Incompatible types in assignment (expression has type "Path", variable has type "SupportsPosixPath")
foo.py:13: error: Incompatible types in assignment (expression has type "Path", variable has type "SupportsPosixPath")

如果我将typehint更改为“Path”（如下），我不会通过mypy或PyCharm linter得到任何错误，但我应该这样做，因为“Path”不支持.ascii_lowercase-

# Python 3.8.5
from typing import Protocol
from pathlib import Path  # , PosixPath


# class SupportsPosixPath(Protocol):
    # def obj(self) -> PosixPath:
        # ...


_home: Path = Path("~")
_application_dir: Path = Path("application")
_data_dir: Path = Path("data")


def do_path_stuff(_home, _application_dir, _data_dir) -> Path:
    _complete_path = _home.joinpath(_application_dir)
    _complete_path = _complete_path.joinpath(_data_dir)
    _complete_path = _complete_path.expanduser()
    _complete_path = (
        _complete_path.ascii_lowercase()
    )  # This should raise a linter error because PosixPath doesn't support ascii_lowercase.
    return _complete_path

在^^^上运行mypy

$ mypy foo.py 
Success: no issues found in 1 source file

Answer 1

感谢@user2357112在评论中对Monica的支持。我不需要创建自己的类型，我需要将类型提示移动到函数中。下面的代码适用于mypi和PyCharm linter-

# Python 3.8.5
from pathlib import Path


_home = Path("~")
_application_dir = Path("application")
_data_dir = Path("data")


def do_path_stuff(_home, _application_dir, _data_dir) -> Path:
    _complete_path: Path = _home.joinpath(_application_dir)
    _complete_path: Path = _complete_path.joinpath(_data_dir)
    _complete_path: Path = _complete_path.expanduser()
    return _complete_path


p = do_path_stuff(_home, _application_dir, _data_dir)
print(p)