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urllib3 PoolManager.urlopen fails with TypeError for http connection if the PoolManager is (Fix)

Fixed
Spec
Package
urllib3
Fixed In
1.26.9
Python
3.8.10
Verdict
Status
Fixed
Safe for prod
No
Risk
Medium
Last verified
2026-02-09
Own content ratio
0.22
#2534 ai connection-leak timeouts Updated: 2026-02-13
Issue #2534

The Fix

pip install urllib3==1.26.9

Based on closed urllib3/urllib3 issue #2534 · 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
@@ -55,6 +55,7 @@ "ssl_context", "key_password", + "server_hostname", ) # Default value for `blocksize` - a new parameter introduced to
repro.py
>> import platform >> import urllib3 >> >> print("OS", platform.platform()) OS Linux-5.11.22-100.fc32.x86_64-x86_64-with-glibc2.2.5 >> print("Python", platform.python_version()) Python 3.8.10 >> print("urllib3", urllib3.__version__) urllib3 1.26.8
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 urllib3==1.26.9\nWhen NOT to use: Do not use this fix if server_hostname is not required for your application.\n\n

Why This Fix Works in Production

  • Trigger: >> import urllib3
  • Mechanism: TypeError occurs due to server_hostname not being accepted by HTTPConnection
  • Why the fix works: Adds support for the server_hostname parameter in the PoolManager, resolving a TypeError when making HTTP requests. (first fixed release: 1.26.9).
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 3.8.10 in real deployments (not just unit tests).
  • TypeError occurs due to server_hostname not being accepted by HTTPConnection
  • Surfaces as: >> import urllib3

Proof / Evidence

  • GitHub issue: #2534
  • Fix PR: https://github.com/urllib3/urllib3/pull/2537
  • First fixed release: 1.26.9
  • Reproduced locally: No (not executed)
  • Last verified: 2026-02-09
  • Confidence: 0.85
  • Did this fix it?: Yes (upstream fix exists)
  • Own content ratio: 0.22

Discussion

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

Jump to Sources Open on GitHub
“As far as I can tell a new version of urllib3 including this fix has not yet been released. 1.26.8 is the latest on pypi.…”
@cdent · 2022-03-15 · confirmation · source
“FYI: This was initially reported in https://github.com/cdent/gabbi/issues/309 .”
@kajinamit · 2022-01-18 · source
“Just adding some more results..”
@kajinamit · 2022-01-18 · source

Failure Signature (Search String)

  • >> import urllib3

Error Message

Stack trace
error.txt
Error Message ------------- >> import urllib3 >> manager = urllib3.PoolManager(server_hostname='foo') >> manager.urlopen('GET', 'http://127.0.0.1') Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/poolmanager.py", line 375, in urlopen response = conn.urlopen(method, u.request_uri, **kw) File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/connectionpool.py", line 692, in urlopen conn = self._get_conn(timeout=pool_timeout) File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/connectionpool.py", line 281, in _get_conn return conn or self._new_conn() File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/connectionpool.py", line 235, in _new_conn conn = self.ConnectionCls( File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/connection.py", line 130, in __init__ _HTTPConnection.__init__(self, *args, **kw) TypeError: __init__() got an unexpected keyword argument 'server_hostname'
Stack trace
error.txt
Error Message ------------- >> import urllib3 >> manager = urllib3.PoolManager(server_hostname='foo') >> manager.urlopen('GET', 'https://127.0.0.1') Traceback (most recent call last): File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/connection.py", line 174, in _new_conn conn = connection.create_connection( File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/util/connection.py", line 95, in create_connection raise err File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/util/connection.py", line 85, in create_connection sock.connect(sa) ConnectionRefusedError: [Errno 111] Connection refused During handling of the above exception, another exception occurred: Traceback (most recent call last): File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/connectionpool.py", line 703, in urlopen httplib_response = self._make_request( File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/connectionpool.py", line 386, in _make_request self._validate_conn(conn) File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/connectionpool.py", line 1040, in _validate_conn conn.connect() File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/connection.py", line 358, in connect conn = self._new_conn() File "/home/tkajinam/virtualenv/foo/lib/python3.8/si ... (truncated) ...
Stack trace
error.txt
Error Message ------------- >> manager = urllib3.PoolManager() >> manager.urlopen('GET', 'http://127.0.0.1') Traceback (most recent call last): File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/connection.py", line 174, in _new_conn conn = connection.create_connection( File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/util/connection.py", line 95, in create_connection raise err File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/util/connection.py", line 85, in create_connection sock.connect(sa) ConnectionRefusedError: [Errno 111] Connection refused During handling of the above exception, another exception occurred: Traceback (most recent call last): File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/connectionpool.py", line 703, in urlopen httplib_response = self._make_request( File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/connectionpool.py", line 398, in _make_request conn.request(method, url, **httplib_request_kw) File "/home/tkajinam/virtualenv/foo/lib/python3.8/site-packages/urllib3/connection.py", line 239, in request super(HTTPConnection, self).request(method, url, body=body, headers=headers) File "/usr/lib64/python3.8/http/client.py", line 1252, in request self._send_request(method, url, body, headers, encode_chunked) File "/usr/lib64/python3 ... (truncated) ...

Minimal Reproduction

repro.py
>> import platform >> import urllib3 >> >> print("OS", platform.platform()) OS Linux-5.11.22-100.fc32.x86_64-x86_64-with-glibc2.2.5 >> print("Python", platform.python_version()) Python 3.8.10 >> print("urllib3", urllib3.__version__) urllib3 1.26.8

Environment

  • Python: 3.8.10
  • urllib3: 1.26.8

What Broke

TypeError prevents HTTP requests from being sent, causing application failures.

Why It Broke

TypeError occurs due to server_hostname not being accepted by HTTPConnection

Fix Options (Details)

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

pip install urllib3==1.26.9

When NOT to use: Do not use this fix if server_hostname is not required for your application.

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/2537

First fixed release: 1.26.9

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

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When NOT to Use This Fix

  • Do not use this fix if server_hostname is not required for your application.

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

  • 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.
  • Track RSS + object counts after deployments; alert on monotonic growth and GC pressure.
  • Add a long-running test that repeats the failing call path and asserts stable memory.

Version Compatibility Table

VersionStatus
1.26.9 Fixed

Related Issues

No related fixes found.

Cluster: urllib3:configuration-error urllib3 hub urllib3 best practices All hubs All clusters
Related clusters: Data consistency SSL handshake Other

Sources

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

Source & Disclaimer: Analysis derived from GitHub Issue #2534. Not affiliated with the library maintainers. Verify before production use.