urllib3 urllib3==1.21: TypeError: unhashable type: 'list'

The Fix

pip install urllib3==1.25

Based on closed urllib3/urllib3 issue #1165 · PR/commit linked

Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.

Jump to Verify Open PR/Commit

@@ -7,6 +7,9 @@ dev (master)
   delivery. (Pull #1154)
 
+* Fixed regression in 1.21 that threw exceptions when users passed the
+  ``socket_options`` flag to the ``PoolManager``.  (Issue #1165)
+

repro.py

2017-04-28T04:26:10.152544966Z   File "/usr/local/lib/python3.5/site-packages/steembase/http_client.py", line 146, in exec
2017-04-28T04:26:10.152552486Z     response = self.request(body=body)
2017-04-28T04:26:10.152560726Z   File "/usr/local/lib/python3.5/site-packages/urllib3/poolmanager.py", line 303, in urlopen
2017-04-28T04:26:10.152585508Z     conn = self.connection_from_host(u.host, port=u.port, scheme=u.scheme)
2017-04-28T04:26:10.152592399Z   File "/usr/local/lib/python3.5/site-packages/urllib3/poolmanager.py", line 219, in connection_from_host
2017-04-28T04:26:10.152599135Z     return self.connection_from_context(request_context)
2017-04-28T04:26:10.152604508Z   File "/usr/local/lib/python3.5/site-packages/urllib3/poolmanager.py", line 232, in connection_from_context
2017-04-28T04:26:10.152610299Z     return self.connection_from_pool_key(pool_key, request_context=request_context)
2017-04-28T04:26:10.152615790Z   File "/usr/local/lib/python3.5/site-packages/urllib3/poolmanager.py", line 245, in connection_from_pool_key
2017-04-28T04:26:10.152621674Z     pool = self.pools.get(pool_key)
2017-04-28T04:26:10.152626932Z   File "/usr/local/lib/python3.5/_collections_abc.py", line 597, in get
2017-04-28T04:26:10.152632427Z     return self[key]
2017-04-28T04:26:10.152637611Z   File "/usr/local/lib/python3.5/site-packages/urllib3/_collections.py", line 53, in __getitem__
2017-04-28T04:26:10.152643188Z     item = self._container.pop(key)
2017-04-28T04:26:10.152648363Z TypeError: unhashable type: 'list'

verify

from urllib3.poolmanager import PoolManager
p = PoolManager(socket_options=[])
p.urlopen('GET', 'https://www.google.com')

fix.md

Option A — Upgrade to fixed release\npip install urllib3==1.25\nWhen NOT to use: Do not use this fix if socket_options is intended to be a list for other functionalities.\n\n

Why This Fix Works in Production

Trigger: TypeError: unhashable type: 'list'
Mechanism: The socket_options parameter was incorrectly passed as a list instead of a tuple, causing a TypeError
Why the fix works: Fixed a regression in urllib3 version 1.21 that caused exceptions when passing the socket_options flag to the PoolManager. (first fixed release: 1.25).

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

Shows up under Python 3.5 in real deployments (not just unit tests).
The socket_options parameter was incorrectly passed as a list instead of a tuple, causing a TypeError
Surfaces as: TypeError: unhashable type: 'list'

Proof / Evidence

GitHub issue: #1165
Fix PR: https://github.com/urllib3/urllib3/pull/1166
First fixed release: 1.25
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.42

Discussion

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

Jump to Sources Open on GitHub

“Thanks for the report. Could you provide a minimal reproducible example? You link to code but there's no mention of how you're using the code…”

@sethmlarson · 2017-04-28 · repro detail · source

“Yeah that's it, here's a minimal verifiable example for maintainers that read this tomorrow: cc: #1016 @jeremycline Goodnight :sleeping:”

@sethmlarson · 2017-04-28 · repro detail · source

“Any attempt to do a http request will do. A simple example: Steem in this case wraps http_client.py (code link above). My speculation is that…”

@Netherdrake · 2017-04-28 · source

“Looks like it's socket_options that needs to be converted into a tuple to be used as a part of a PoolKey because lists aren't hash-able?…”

@sethmlarson · 2017-04-28 · source

Failure Signature (Search String)

TypeError: unhashable type: 'list'

Error Message

Stack trace

error.txt

Error Message
-------------
TypeError: unhashable type: 'list'

Minimal Reproduction

repro.py

2017-04-28T04:26:10.152544966Z   File "/usr/local/lib/python3.5/site-packages/steembase/http_client.py", line 146, in exec
2017-04-28T04:26:10.152552486Z     response = self.request(body=body)
2017-04-28T04:26:10.152560726Z   File "/usr/local/lib/python3.5/site-packages/urllib3/poolmanager.py", line 303, in urlopen
2017-04-28T04:26:10.152585508Z     conn = self.connection_from_host(u.host, port=u.port, scheme=u.scheme)
2017-04-28T04:26:10.152592399Z   File "/usr/local/lib/python3.5/site-packages/urllib3/poolmanager.py", line 219, in connection_from_host
2017-04-28T04:26:10.152599135Z     return self.connection_from_context(request_context)
2017-04-28T04:26:10.152604508Z   File "/usr/local/lib/python3.5/site-packages/urllib3/poolmanager.py", line 232, in connection_from_context
2017-04-28T04:26:10.152610299Z     return self.connection_from_pool_key(pool_key, request_context=request_context)
2017-04-28T04:26:10.152615790Z   File "/usr/local/lib/python3.5/site-packages/urllib3/poolmanager.py", line 245, in connection_from_pool_key
2017-04-28T04:26:10.152621674Z     pool = self.pools.get(pool_key)
2017-04-28T04:26:10.152626932Z   File "/usr/local/lib/python3.5/_collections_abc.py", line 597, in get
2017-04-28T04:26:10.152632427Z     return self[key]
2017-04-28T04:26:10.152637611Z   File "/usr/local/lib/python3.5/site-packages/urllib3/_collections.py", line 53, in __getitem__
2017-04-28T04:26:10.152643188Z     item = self._container.pop(key)
2017-04-28T04:26:10.152648363Z TypeError: unhashable type: 'list'

Environment

Python: 3.5
urllib3: 1.21

What Broke

HTTP requests fail with a TypeError when socket_options is a list.

Why It Broke

The socket_options parameter was incorrectly passed as a list instead of a tuple, causing a TypeError

Fix Options (Details)

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

pip install urllib3==1.25

When NOT to use: Do not use this fix if socket_options is intended to be a list for other functionalities.

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

Fix reference: https://github.com/urllib3/urllib3/pull/1166

First fixed release: 1.25

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

When NOT to Use This Fix

Do not use this fix if socket_options is intended to be a list for other functionalities.

Verify Fix

verify

from urllib3.poolmanager import PoolManager
p = PoolManager(socket_options=[])
p.urlopen('GET', 'https://www.google.com')

Did This Fix Work in Your Case?

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

Prevention

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.

Version Compatibility Table

Version	Status
1.25	Fixed

Related Issues

No related fixes found.

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Sources

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

urllib3 urllib3==1.21: TypeError: unhashable type: 'list' (Fix)