pathlib.Path的简单子类化错误：没有_flavour属性

由真凝心发布于 2020-05-09 07:41:22

我正在尝试从pathlib继承Path，但是在实例化时出现以下错误而失败

from pathlib import Path
class Pl(Path):
    def __init__(self, *pathsegments: str):
        super().__init__(*pathsegments)

实例化时出错

AttributeError: type object 'Pl' has no attribute '_flavour'

et_ea

2020-05-09 07:41:22

Part of the problem is that the Path class implements some conditional logic in __new__ that doesn't really lend itself to subclassing. Specifically:

    def __new__(cls, *args, **kwargs):
        if cls is Path:
            cls = WindowsPath if os.name == 'nt' else PosixPath

This sets the type of the object you get back from Path(...) to either PosixPath or WindowsPath, but only if cls is Path, which will never be true for a subclass of Path.

That means within the __new__ function, cls won't have the_flavourattribute (which is set explicitly for the*WindowsPath and *PosixPath classes), because your Pl class doesn't have a _flavour attribute.

I think you would be better off explicitly subclassing one of the other classes, such as PosixPath or WindowsPath.

xnemo

2020-05-09 07:41:22

Path is somewhat of an abstract class that is actually instantiated as on of two possible subclasses depending on the OS:

PosixPath or WindowsPath

https://docs.python.org/3/library/pathlib.html

This base class looks for an internal (private) class variable to determine what type of object it actually is, and this variable is called _flavour

您有两种选择：

从一个具体的子类派生您的类。
这是最好的选择，因为它将节省您处理未记录的库内部文件的时间，并确保您的代码不会在库的不同版本上中断。
如果您希望代码跨平台，则需要根据操作系统定义不同的类。

该代码将如下所示：

import os

if os.name == 'posix':
    base = PosixPath
else:
    base = Path

class P1(base):
    # rest of your code here

Alternatively fill in the class variable yourself.
This is not recommended as you will be using undocumented elements that could break at any time with any change to the library, but it will allow you to inherit from Path directly.

请注意，如果您决定使用此方法，可能还会有其他问题！

import os

class P1(Path):
    _flavour = _PosixFlavour() if os.name = 'posix' else _WindowsFlavour()

    # rest of your code here

真凝心

这家伙很懒，什么都没留下

积分
0
话题
0
评论
3192
注册排名
1957