python - AttributeError:'str'对象没有属性'errno'

我在ClientConnectionError生成的multiprocessing.Queue中放置了一个asyncio异常。我这样做是为了将在asyncio land中生成的异常传递回另一个线程/进程中的客户端。
我的假设是，此异常发生在从队列中读取异常的反序列化过程中。如果不这样做的话，很难达到目的。

Traceback (most recent call last):
  File "model_neural_simplified.py", line 318, in <module>
    main(**arg_parser())
  File "model_neural_simplified.py", line 314, in main
    globals()[command](**kwargs)
  File "model_neural_simplified.py", line 304, in predict
    next_neural_data, next_sample = reader.get_next_result()
  File "/project_neural_mouse/src/asyncs3/s3reader.py", line 174, in get_next_result
    result = future.result()
  File "/usr/lib/python3.6/concurrent/futures/_base.py", line 432, in result
    return self.__get_result()
  File "/usr/lib/python3.6/concurrent/futures/_base.py", line 384, in __get_result
    raise self._exception
  File "/usr/lib/python3.6/concurrent/futures/thread.py", line 56, in run
    result = self.fn(*self.args, **self.kwargs)
  File "model_neural_simplified.py", line 245, in read_sample
    f_bytes = s3f.read(read_size)
  File "/project_neural_mouse/src/asyncs3/s3reader.py", line 374, in read
    size, b = self._issue_request(S3Reader.READ, (self.url, size, self.position))
  File "/project_neural_mouse/src/asyncs3/s3reader.py", line 389, in _issue_request
    response = self.communication_channels[uuid].get()
  File "/usr/lib/python3.6/multiprocessing/queues.py", line 113, in get
    return _ForkingPickler.loads(res)
  File "/usr/local/lib/python3.6/dist-packages/aiohttp/client_exceptions.py", line 133, in __init__
    super().__init__(os_error.errno, os_error.strerror)
AttributeError: 'str' object has no attribute 'errno'

我想问这个问题有点难，但是有人知道这个问题吗？
python 3.6.8，aiohttp.\uuu版本=3.6.0
更新：
我成功地再现了这个问题（塞缪尔在评论中提到了改进最小可重复性测试用例的功劳，后来xtreak在bugs.python.org上提到了进一步将其提取到pickle-only测试用例中的功劳）：

import pickle

ose = OSError(1, 'unittest')

class SubOSError(OSError):

    def __init__(self, foo, os_error):
        super().__init__(os_error.errno, os_error.strerror)

cce = SubOSError(1, ose)
cce_pickled = pickle.dumps(cce)
pickle.loads(cce_pickled)


./python.exe ../backups/bpo38254.py
Traceback (most recent call last):
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/../backups/bpo38254.py", line 12, in <module>
    pickle.loads(cce_pickled)
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/../backups/bpo38254.py", line 8, in __init__
    super().__init__(os_error.errno, os_error.strerror)
AttributeError: 'str' object has no attribute 'errno'

参考文献：
https://github.com/aio-libs/aiohttp/issues/4077
https://bugs.python.org/issue38254

最佳答案

OSError具有a custom __reduce__ implementation；不幸的是，对于与预期参数不匹配的子类，它不是子类友好的。通过手动调用__reduce__可以看到酸洗的中间状态：

>>> SubOSError.__reduce__(cce)
(modulename.SubOSError, (1, 'unittest'))

tuple的第一个元素是可调用的，第二个元素是要传递的参数的tuple。所以当它试图重新创建您的类时，它会：

modulename.SubOSError(1, 'unittest')

已经丢失了您最初创建时使用的OSError的信息。
如果必须接受与OSError.__reduce__/OSError.__init__期望不匹配的参数，则需要编写自己的__reduce__重写以确保pickle了正确的信息。一个简单的版本可能是：

class SubOSError(OSError):

    def __init__(self, foo, os_error):
        self.foo = foo  # Must preserve information for pickling later
        super().__init__(os_error.errno, os_error.strerror)

    def __reduce__(self):
        # Pickle as type plus tuple of args expected by type
        return type(self), (self.foo, OSError(*self.args))

采用这种设计，SubOSError.__reduce__(cce)现在将返回：

(modulename.SubOSError, (1, PermissionError(1, 'unittest')))

其中tuple的第二个元素是重新创建实例所需的正确参数（预期会从OSError更改为PermissionError；OSError实际上会根据errno返回自己的子类）。