Python 输入 : Describe common properties

Question

我有一些自动生成的代码，它们定义了许多具有公共(public)属性的类，例如不幸的是，它们没有基类、接口(interface)等。

class A:
    errors = []

class B
    errors = []

我如何描述它的类型？我无法轻易更改所有这些类型。

def validate(obj: ???):
    if errors:
        raise Exception("something wrong")

Answer 1

您需要定义一个协议(protocol)，通过 typing.Protocol 完成Python 3.8 或更高版本(早期版本可以在 Protocol 模块中找到 typing_extensions。)

from typing import Protocol


class HasErrors(Protocol):
    errors: list


# Requires an object whose type supports the HasErrors
# protocol, namely one with a list-valued class attribute 
# named "errors"
def validate(obj: HasErrors):
    if obj.errors:
        raise Exception("something wrong")


class GoodClass:
    errors: List[Any] = []

class BadClass1:
    pass

class BadClass2:
    errors: int = 3

validate(GoodClass())  # will pass
validate(BadClass1())  # will not pass; no errors attribute
validate(BadClass2())  # will not pass; errors attribute has wrong type