SlackApiError cannot be unpickled

SlackApiError raises an error when trying to unpickle it.

This is particularly annoying in a Celery task since another bug in celery will cause the whole worker node to fail.

The Slack SDK version

2.9.4

Python runtime version

3.11.0

OS info

ProductName: macOS
ProductVersion: 13.0
BuildVersion: 22A380
Darwin Kernel Version 22.1.0: Sun Oct 9 20:15:09 PDT 2022; root:xnu-8792.41.9~2/RELEASE_ARM64_T6000

Steps to reproduce:

import pickle
from slack.errors import SlackApiError

e = SlackApiError("Internal server error", "<response>")

dumped = pickle.dumps(e)
pickle.loads(dumped) 

Expected result:

No error.

Actual result:

Traceback (most recent call last):
  File "/private/tmp/pickle_exc/bug.py", line 7, in <module>
    pickle.loads(dumped)
TypeError: SlackApiError.__init__() missing 1 required positional argument: 'response'

Solution

The SlackApiError could be implemented in such a way that the constructor accepts only the message, and the response defaults to None. Then the string representation can be delegated to __str__:

class SlackApiError(Exception):

    def __init__(self, message, response=None):
        super().__init__(message)
        self.response = response
    
    def __str__(self):
        return f"{self.args[0]}\nThe server responded with: {self.response}"

Start with the SlackApiError definition and run the pickle reproduction shown in the issue on Python 3.11. Check how the exception is initialized and represented, then verify that pickling and unpickling preserve the message and response without raising TypeError.