RetryError cannot be serialized with pickle

[mezgerj]

Currently, RetryError is unpickleable. To ensure that exceptions raised from the tenacity library are pickle-able they should provide the original arguments it was instantiated with in its .args attribute.This affects the ability to use tenacity inside of a celery task for example. I am working on a PR for this issue.

[crdoconnor]

This is causing me headaches too. It makes tenacity not usable with celery.

[Alexander3]

I still have this issue using tenacity==7.0.0 and celery==4.4.7
I tried updating, but I get the same error in tenacity==8.0.1

from celery import shared_task
from tenacity import (
    retry,
    retry_if_exception_type,
    stop_after_attempt,
)

@retry(
    retry=retry_if_exception_type(ValueError), stop=stop_after_attempt(1),
)
def foo():
    raise ValueError()


@shared_task()
def test_exp():
    foo()

Calling this task results in

[2021-10-08 19:17:51,368: ERROR/ForkPoolWorker-7] Task apps.main.tasks.test_exp[539feed0-0c87-4a61-ad2a-ba158e7854a6] raised unexpected: RetryError('<Future at 0x7fb0ac4797f0 state=finished raised ValueError>')
Traceback (most recent call last):
  File "/home/bond/.virtualenvs/backend-4I_U3jTL/lib/python3.8/site-packages/celery/app/trace.py", line 412, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/home/bond/.virtualenvs/backend-4I_U3jTL/lib/python3.8/site-packages/celery/app/trace.py", line 704, in __protected_call__
    return self.run(*args, **kwargs)
  File "/home/bond/.virtualenvs/backend-4I_U3jTL/lib/python3.8/site-packages/sentry_sdk/integrations/celery.py", line 197, in _inner
    reraise(*exc_info)
  File "/home/bond/.virtualenvs/backend-4I_U3jTL/lib/python3.8/site-packages/sentry_sdk/_compat.py", line 54, in reraise
    raise value
  File "/home/bond/.virtualenvs/backend-4I_U3jTL/lib/python3.8/site-packages/sentry_sdk/integrations/celery.py", line 192, in _inner
    return f(*args, **kwargs)
  File "/home/bond/work/current/nadii/NadiiUI/backend/apps/main/tasks.py", line 151, in test_exp
    foo()
  File "/home/bond/.virtualenvs/backend-4I_U3jTL/lib/python3.8/site-packages/tenacity/__init__.py", line 339, in wrapped_f
    return self(f, *args, **kw)
  File "/home/bond/.virtualenvs/backend-4I_U3jTL/lib/python3.8/site-packages/tenacity/__init__.py", line 430, in __call__
    do = self.iter(retry_state=retry_state)
  File "/home/bond/.virtualenvs/backend-4I_U3jTL/lib/python3.8/site-packages/tenacity/__init__.py", line 379, in iter
    six.raise_from(retry_exc, fut.exception())
  File "<string>", line 3, in raise_from
tenacity.RetryError: <Future at 0x7fb0ac4797f0 state=finished raised ValueError>
[2021-10-08 19:17:51,378: ERROR/MainProcess] Task handler raised error: <MaybeEncodingError: Error sending result: '"(1, <ExceptionInfo: RetryError('<Future at 0x7fb0ac4797f0 state=finished raised ValueError>')>, None)"'. Reason: ''PicklingError("Can\'t pickle <class \'tenacity.RetryError\'>: it\'s not the same object as tenacity.RetryError")''.>
Traceback (most recent call last):
  File "/home/bond/.virtualenvs/backend-4I_U3jTL/lib/python3.8/site-packages/billiard/pool.py", line 366, in workloop
    put((READY, (job, i, result, inqW_fd)))
  File "/home/bond/.virtualenvs/backend-4I_U3jTL/lib/python3.8/site-packages/billiard/queues.py", line 366, in put
    self.send_payload(ForkingPickler.dumps(obj))
  File "/home/bond/.virtualenvs/backend-4I_U3jTL/lib/python3.8/site-packages/billiard/reduction.py", line 56, in dumps
    cls(buf, protocol).dump(obj)
billiard.pool.MaybeEncodingError: Error sending result: '"(1, <ExceptionInfo: RetryError('<Future at 0x7fb0ac4797f0 state=finished raised ValueError>')>, None)"'. Reason: ''PicklingError("Can\'t pickle <class \'tenacity.RetryError\'>: it\'s not the same object as tenacity.RetryError")''.