我在Python中学习OOP，并遇到了一个问题。如何从对象方法中正确访问受保护的类属性？示例代码：

Question

error: Cannot assign to class variable "_foo" via instance [misc]

，让我们尝试一下：

self.__class__._foo

。再次错过！现在拉夫发誓：

SLF001 Private member accessed: `_foo`
   |
 9 |     def baz(self, num: int) -> None:
10 |         self.__class__._foo = num
   |         ^^^^^^^^^^^^^^^^^^^ SLF001
11 |
12 | if __name__ == "__main__":
   |

那么正确的方法是什么？

问题不是该变量受到保护，而是它是一个

ClassVar

。

因此，您可以将变量定义为：

_foo: int = 2

Answer 1

ClassVar

：

@_SpecialForm
def ClassVar(self, parameters):
    """Special type construct to mark class variables.

    An annotation wrapped in ClassVar indicates that a given
    attribute is intended to be used as a class variable and
    should not be set on instances of that class. Usage::

      class Starship:
          stats: ClassVar[Dict[str, int]] = {} # class variable
          damage: int = 10                     # instance variable

    ClassVar accepts only types and cannot be further subscribed.

    Note that ClassVar is not a class itself, and should not
    be used with isinstance() or issubclass().
    """
    item = _type_check(parameters, f'{self} accepts only single type.')
    return _GenericAlias(self, (item,))