Celery using couchdb backend throws TypeError: a bytes-like

The Fix

pip install celery==5.1.1

Based on closed celery/celery issue #6781 · PR/commit linked

Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.

Jump to Verify Open PR/Commit

@@ -75,6 +75,7 @@ def connection(self):
 
     def get(self, key):
+        key = bytes_to_str(key)
         try:
             return self.connection.get(key)['value']

repro.py

from celery import Celery
app = Celery("tasks", broker="pyamqp://....", backend="couchdb://...")
@app.task
def add(x, y):
    return x + y

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install celery==5.1.1\nWhen NOT to use: This fix should not be applied if the key is expected to remain a bytes-like object.\n\n

Why This Fix Works in Production

Trigger: [2021-05-23 19:34:24,965: ERROR/MainProcess] Pool callback raised exception: TypeError("a bytes-like object is required, not 'str'")
Mechanism: The couchdb backend's get() method was not converting the key to a string, causing a TypeError
Why the fix works: Fixes the couchdb backend call get() method by converting the key to a string, addressing the TypeError encountered in issue #6781. (first fixed release: 5.1.1).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

Triggered by an upgrade/regression window: 1.6.5 breaks; 5.1.1 is the first fixed release.
Shows up under Python 3.9 in real deployments (not just unit tests).
The couchdb backend's get() method was not converting the key to a string, causing a TypeError
Surfaces as: [2021-05-23 19:34:24,965: ERROR/MainProcess] Pool callback raised exception: TypeError("a bytes-like object is required, not 'str'")

Proof / Evidence

GitHub issue: #6781
Fix PR: https://github.com/celery/celery/pull/6782
First fixed release: 5.1.1
Affected versions: 1.6.5
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.44

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“Hey @worldworm :wave:, Thank you for opening an issue”

@open-collective-bot · 2021-05-23 · source

“I tried my hand at a fix once. For other backends, it seems that the key is also converted to a string.”

@worldworm · 2021-05-23 · source

Failure Signature (Search String)

[2021-05-23 19:34:24,965: ERROR/MainProcess] Pool callback raised exception: TypeError("a bytes-like object is required, not 'str'")

Error Message

Stack trace

error.txt

Error Message
-------------
[2021-05-23 19:34:24,965: ERROR/MainProcess] Pool callback raised exception: TypeError("a bytes-like object is required, not 'str'")
Traceback (most recent call last):
  File "/config/.local/lib/python3.9/site-packages/billiard/pool.py", line 1796, in safe_apply_callback
    fun(*args, **kwargs)
  File "/config/.local/lib/python3.9/site-packages/celery/worker/request.py", line 567, in on_failure
    self.task.backend.mark_as_failure(
  File "/config/.local/lib/python3.9/site-packages/celery/backends/base.py", line 171, in mark_as_failure
    self.store_result(task_id, exc, state,
  File "/config/.local/lib/python3.9/site-packages/celery/backends/base.py", line 477, in store_result
    self._store_result(task_id, result, state, traceback,
  File "/config/.local/lib/python3.9/site-packages/celery/backends/base.py", line 898, in _store_result
    current_meta = self._get_task_meta_for(task_id)
  File "/config/.local/lib/python3.9/site-packages/celery/backends/base.py", line 920, in _get_task_meta_for
    meta = self.get(self.get_key_for_task(task_id))
  File "/config/.local/lib/python3.9/site-packages/celery/backends/couchdb.py", line 79, in get
    return self.connection.get(key)['value']
  File "/config/.local/lib/python3.9/site-packages/pycouchdb/client.py", line 345, in get
    (resp, result) = self.resource(*_id_to_path(doc_id)).get(params=params)
  File "/config/.local/lib/p
... (truncated) ...

Minimal Reproduction

repro.py

from celery import Celery
app = Celery("tasks", broker="pyamqp://....", backend="couchdb://...")
@app.task
def add(x, y):
    return x + y

Environment

Python: 3.9

What Broke

CouchDB backend calls resulted in TypeErrors, preventing successful data retrieval.

Why It Broke

The couchdb backend's get() method was not converting the key to a string, causing a TypeError

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install celery==5.1.1

When NOT to use: This fix should not be applied if the key is expected to remain a bytes-like object.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/celery/celery/pull/6782

First fixed release: 5.1.1

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix should not be applied if the key is expected to remain a bytes-like object.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
Pin production dependencies and upgrade only with a reproducible test that hits the failing path.

Version Compatibility Table

Version	Status
1.6.5	Broken
5.1.1	Fixed

Related Issues

No related fixes found.

Cluster: celery:configuration-error Celery hub Celery best practices All hubs All clusters

Related clusters: Data consistency Duplicates Duplicate processing

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

Celery using couchdb backend throws TypeError: a bytes-like object is required, not 'str' (Fix)