Checklist

• I have verified that the issue exists against the master branch of Celery.
• This has already been asked to the discussion group first.
• I have read the relevant section in the
  contribution guide
  on reporting bugs.
• I have checked the issues list
  for similar or identical bug reports.
• I have checked the pull requests list
  for existing proposed fixes.
• I have checked the commit log
  to find out if the bug was already fixed in the master branch.
• I have included all related issues and possible duplicate issues
  in this issue (If there are none, check this box anyway).

Mandatory Debugging Information

• I have included the output of celery -A proj report in the issue.
  (if you are not able to do this, then at least specify the Celery
  version affected).
• I have verified that the issue exists against the master branch of Celery.
• I have included the contents of pip freeze in the issue.
• I have included all the versions of all the external dependencies required
  to reproduce this bug.

Optional Debugging Information

• I have tried reproducing the issue on more than one Python version
  and/or implementation.
• I have tried reproducing the issue on more than one message broker and/or
  result backend.
• I have tried reproducing the issue on more than one version of the message
  broker and/or result backend.
• I have tried reproducing the issue on more than one operating system.
• I have tried reproducing the issue on more than one workers pool.
• I have tried reproducing the issue with autoscaling, retries,
  ETA/Countdown & rate limits disabled.
• I have tried reproducing the issue after downgrading
  and/or upgrading Celery and its dependencies.

Related Issues and Possible Duplicates

Related Issues

• Introduced by 0463bff
• Add retry on recoverable exception for the backend #6122

Possible Duplicates

• None

Environment & Settings

Celery version: 4.4.4

Steps to Reproduce

1. Upgrade from Celery 4.4.3 to 4.4.4
2. Get ModuleNotFoundError: No module named 'future' eror

Required Dependencies

• Minimal Python Version: N/A or Unknown
• Minimal Celery Version: N/A or Unknown
• Minimal Kombu Version: N/A or Unknown
• Minimal Broker Version: N/A or Unknown
• Minimal Result Backend Version: N/A or Unknown
• Minimal OS and/or Kernel Version: N/A or Unknown
• Minimal Broker Client Version: N/A or Unknown
• Minimal Result Backend Client Version: N/A or Unknown

Python Packages

Other Dependencies

Minimally Reproducible Test Case

Expected Behavior

It would work after upgrade. In case new dependencies were introduced, these should be installed.

Actual Behavior

 weblate_1   |   File "/usr/local/lib/python3.7/dist-packages/celery/backends/redis.py", line 25, in <module>
weblate_1   |     from .base import BaseKeyValueStoreBackend
weblate_1   |   File "/usr/local/lib/python3.7/dist-packages/celery/backends/base.py", line 10, in <module>
weblate_1   |     from future.utils import raise_with_traceback
weblate_1   | ModuleNotFoundError: No module named 'future'

See https://github.com/WeblateOrg/docker/runs/733499300