如何使用超类调用键入 Python mixin？

Question

我正在尝试在我的项目中使用FieldMixin来自这个答案的答案，但我无法让它通过mypy检查。当前代码：

class DynamicFieldsMixin(Serializer):
    context: Dict[str, Any]

    def get_field_names(
        self, declared_fields: OrderedDict, info: FieldInfo
    ) -> Set[str]:
        field_names: Set[str] = self.context.get(
            "fields",
            super().get_field_names(declared_fields, info)
        )
        return field_names

继承自rest_framework.serializers.Serializer似乎很奇怪，我想知道是否有办法避免这种情况，因为它意味着要混合到实际的Serializer类中。仅删除超类会导致此错误：

错误：“get_field_names”在超类中未定义

mypy 配置：

[mypy]
check_untyped_defs = true
disallow_untyped_defs = true
ignore_missing_imports = true
no_implicit_optional = true
warn_redundant_casts = true
warn_return_any = true
warn_unused_ignores = true

Answer 1

您可以仅出于类型检查的目的引入基类：

import typing
from typing import Any, Dict, List, Mapping, TypeVar
from rest_framework.fields import Field
from rest_framework.serializers import ModelSerializer
from rest_framework.utils.model_meta import FieldInfo


if typing.TYPE_CHECKING:
    _Base = ModelSerializer
else:
    _Base = object


class DynamicFieldsMixin(_Base):
    context: Dict[str, Any]

    def get_field_names(self, declared_fields: Mapping[str, Field], info: FieldInfo) -> List[str]:
        field_names = super().get_field_names(declared_fields, info)
        # Revealed type is 'builtins.list[builtins.str]'
        reveal_type(field_names)
        return field_names