Python中正确导入SupportsWrite类型提示的方法及运行报错解决

你遇到的问题是因为_typeshed是Python类型检查器（如mypy）的内部模块，无法在运行时导入。以下是几种正确获取SupportsWrite类型提示的方法：

方法1：使用标准库typing模块的SupportsWrite（Python 3.8+） #

从Python 3.8开始，SupportsWrite正式被纳入typing模块，可以直接导入使用：

from collections import UserString
from typing import Literal, SupportsWrite

class Strool(UserString):
    def __init__(self, string) -> None:
        super().__init__(string)
    
    def print(self, end: str | None = "\n", file: SupportsWrite[str] | None = None, flush: Literal[False] = False):
        print(self.data, end=end, file=file, flush=flush)

方法2：自定义SupportsWrite协议（兼容Python 3.6+） #

如果你的Python版本低于3.8，可以通过typing.Protocol自定义一个兼容的类型协议，效果和_typeshed.SupportsWrite完全一致：

from collections import UserString
from typing import Literal, Protocol, Any

class SupportsWrite(Protocol):
    def write(self, s: str) -> Any:
        ...

class Strool(UserString):
    def __init__(self, string) -> None:
        super().__init__(string)
    
    def print(self, end: str | None = "\n", file: SupportsWrite | None = None, flush: Literal[False] = False):
        print(self.data, end=end, file=file, flush=flush)

方法3：使用io.TextIO作为替代 #

如果你不需要极致宽泛的类型兼容，也可以直接使用io.TextIO类型，这是原生print函数file参数的官方类型提示之一：

from collections import UserString
from typing import Literal
import io

class Strool(UserString):
    def __init__(self, string) -> None:
        super().__init__(string)
    
    def print(self, end: str | None = "\n", file: io.TextIO | None = None, flush: Literal[False] = False):
        print(self.data, end=end, file=file, flush=flush)

补充说明 #

• 如果你只是需要类型检查时生效，也可以使用if typing.TYPE_CHECKING条件导入，避免运行时加载_typeshed：

from collections import UserString
from typing import Literal
import typing

if typing.TYPE_CHECKING:
    from _typeshed import SupportsWrite

class Strool(UserString):
    def __init__(self, string) -> None:
        super().__init__(string)
    
    def print(self, end: str | None = "\n", file: "SupportsWrite[str]" | None = None, flush: Literal[False] = False):
        print(self.data, end=end, file=file, flush=flush)

这种方式下，类型检查器会识别SupportsWrite，但运行时不会尝试导入_typeshed，也不会报错。

内容的提问来源于stack exchange，提问作者Carlos González