如何解决将PipelineTask实例传入自身add方法时报NameError的问题

我想要将PipelineTask类的实例传入该类自身的PipelineTask.add方法，但运行时触发NameError，提示PipelineTask未定义。
我推测该问题是因为PipelineTask要在PipelineTask.__init__()调用完成后才会完成绑定。

class Task(BaseModel, abc.ABC):
    id: str

    @abc.abstractmethod
    async def run(self):
        pass


class PipelineTask(Task):
    @abc.abstractmethod
    async def run(self):
        pass

    def add(self, task: PipelineTask):
        ## TODO: how do a pass a instance of self here?
        next = self
        if self.next == None:
            self.next = task
            next = self.next
        else:
            current = self.next
            while current != None:
                current = current.next
            next = current
            current.next = next
        return self

class Pipeline(BaseModel):
    """
    Pipeline execute a sequence of tasks

    ...
    init = PipelineTask(id=0)
    pipeline = Pipeline(init=PrepareDataPipelineTask(id='prepare'))
    pipeline.add(ExecutePipelineTask(id='execute')).add(CollectResultsPipelineTask(id='collect'))
    pipeline.run()
    ...
    """

    # The pipelines innitial task
    init: PipelineTask

    async def run(self):
        await self.init.run()
        has_next = self.init.next != None
        next = self.init
        while has_next:
            next = next.next
            await next.run()
            has_next = next.next != None

    ## Adds a task to the end of the pipeline
    async def add(self, next: PipelineTask):
        """add Task to the end of the pipeline"""
        self.init.add(next)


class StdoutTask(PipelineTask):
    async def run(self):
        print(f"[Worker {self.id}] testing...")


async def test_create_pipeline():
    tasks = (
        StdoutTask(id=1, next=None)
        .add(StdoutTask(id=2, next=None))
        .add(StdoutTask(id=3, next=None))
    )
    pipeline = Pipeline(init=tasks)
    await pipeline.run()

示例用法：

class StdoutTask(PipelineTask):
    async def run(self):
        print(f"[Worker {self.id}] testing...")

@pytest.mark.asyncio
async def test_create_pipeline():
    tasks = StdoutTask(id=1).add(StdoutTask(id=2)).add(StdoutTask(id=3))
    pipeline = Pipeline(init=tasks)
    await pipeline.run()
    pass

我曾尝试过两种解决方法都没有成功：

• 移除task的类型标注，运行后触发AttributeError，提示对象不存在next属性：

def add(self, task):
    ...

• 修改task.__class__ = PipelineTask，但该操作只能新增对应方法，无法补全属性。

以下是可单文件运行的问题复现代码：

from pydantic import BaseModel
import abc
import asyncio


class Task(BaseModel, abc.ABC):
    id: str

    @abc.abstractmethod
    async def run(self):
        pass


class PipelineTask(Task):
    @abc.abstractmethod
    async def run(self):
        pass

    def add(self, task: PipelineTask):
        ## TODO: how do a pass a instance of self here?
        next = self
        if self.next == None:
            self.next = task
            next = self.next
        else:
            current = self.next
            while current != None:
                current = current.next
            next = current
            current.next = next
        return self


class Pipeline(BaseModel):
    """
    Pipeline execute a sequence of tasks

    ...
    init = PipelineTask(id=0)
    pipeline = Pipeline(init=PrepareDataPipelineTask(id='prepare'))
    pipeline.add(ExecutePipelineTask(id='execute')).add(CollectResultsPipelineTask(id='collect'))
    pipeline.run()
    ...
    """

    # The pipelines innitial task
    init: PipelineTask

    async def run(self):
        await self.init.run()
        has_next = self.init.next != None
        next = self.init
        while has_next:
            next = next.next
            await next.run()
            has_next = next.next != None

    ## Adds a task to the end of the pipeline
    async def add(self, next: PipelineTask):
        """add Task to the end of the pipeline"""
        self.init.add(next)


class StdoutTask(PipelineTask):
    async def run(self):
        print(f"[Worker {self.id}] testing...")


async def test_create_pipeline():
    tasks = (
        StdoutTask(id=1, next=None)
        .add(StdoutTask(id=2, next=None))
        .add(StdoutTask(id=3, next=None))
    )
    pipeline = Pipeline(init=tasks)
    await pipeline.run()

结合字符串形式的类型前向引用解决NameError，同时使用getattr读取属性避免AttributeError，修改后的代码如下：

def add(self, task: "PipelineTask"):
    next = getattr(self, "next", None)
    if self.next == None:
        self.next = task
        next = self.next
    else:
        current = getattr(self, "next", None)
        while current != None:
            current = getattr(current, "next", None)
        next = getattr(current, "next", None)
        current.next = next
    return self

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