python - 属性错误 : 'str' object has no attribute 'errno'

Question

我在 asyncio 生成的 multiprocessing.Queue 中放置了一个 ClientConnectionError 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。

我的假设是这个异常发生在反序列化过程中从队列中读取异常。否则看起来几乎不可能到达。

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'

我觉得这个问题很难问，但是有人知道这个问题吗？

Python 3.6.8, aiohttp.__version__ == 3.6.0

更新:

我设法重现了这个问题(感谢 Samuel 在评论中改进了最小可重现的测试用例，后来在 bugs.python.org 上的 xtreak 将其进一步提炼为 pickle-only 测试用例):

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'

引用资料:

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

Answer 1

OSError 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。您可以通过手动调用 __reduce__ 来查看酸洗的中间状态:

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

tuple 的第一个元素是要调用的可调用对象，第二个是要传递的参数的 tuple。因此，当它尝试重新创建您的类时，它会:

modulename.SubOSError(1, 'unittest')

丢失了有关您最初创建时使用的 OSError 的信息。

如果您必须接受与 OSError.__reduce__/OSError.__init__ 期望不匹配的参数，您将需要编写自己的 __reduce__ 覆盖以确保腌制正确的信息。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(从 OSError 到 PermissionError 的变化是预期的； OSError 实际上根据errno 返回它自己的子类。