urllib3 "AttributeError: 'NoneType' object has no attribute

The Fix

pip install urllib3==1.25

Based on closed urllib3/urllib3 issue #355 · 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

@@ -2,7 +2,10 @@
 from urllib3.poolmanager import PoolManager
 from urllib3 import connection_from_url
-from urllib3.exceptions import ClosedPoolError
+from urllib3.exceptions import (
+    ClosedPoolError,

repro.py

>> import urllib3
>> http = urllib3.PoolManager()
>> r = http.request('GET', 'http://@')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../urllib3/request.py", line 75, in request
    **urlopen_kw)
  File ".../urllib3/request.py", line 88, in request_encode_url
    return self.urlopen(method, url, **urlopen_kw)
  File ".../urllib3/poolmanager.py", line 145, in urlopen
    conn = self.connection_from_host(u.host, port=u.port, scheme=u.scheme)
  File ".../urllib3/poolmanager.py", line 119, in connection_from_host
    pool = self._new_pool(scheme, host, port)
  File ".../urllib3/poolmanager.py", line 86, in _new_pool
    return pool_cls(host, port, **kwargs)
  File ".../urllib3/connectionpool.py", line 226, in __init__
    ConnectionPool.__init__(self, host, port)
  File ".../urllib3/connectionpool.py", line 156, in __init__
    host = host.strip('[]')
AttributeError: 'NoneType' object has no attribute 'strip'

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==1.25\nWhen NOT to use: Do not use this fix if the application relies on None being a valid host.\n\n

Why This Fix Works in Production

Trigger: >> import urllib3
Mechanism: The connection_from_host method assumes host will never be None, leading to an AttributeError
Why the fix works: Raises a LocationParseError if the host is None, addressing the issue of handling malformed URLs. (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

The connection_from_host method assumes host will never be None, leading to an AttributeError
Surfaces as: >> import urllib3

Proof / Evidence

GitHub issue: #355
Fix PR: https://github.com/urllib3/urllib3/pull/357
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: 0.35

Discussion

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

Jump to Sources Open on GitHub

“Sounds reasonable to me, what do you think @shazow?”

@kevinburke · 2014-03-13 · source

“On thinking about it a little more, maybe it's better to leave parse_url alone - it's documented to be usable for relative URLs after all”

@zackw · 2014-03-14 · source

“Hmm. IMO parse_url should parse an empty-host string if possible as host=None. At that point, the Connection-related class should raise the appropriate exception. What do…”

@shazow · 2014-03-14 · source

Failure Signature (Search String)

>> import urllib3

Error Message

Stack trace

error.txt

Error Message
-------------
>> import urllib3
>> http = urllib3.PoolManager()
>> r = http.request('GET', 'http://@')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../urllib3/request.py", line 75, in request
    **urlopen_kw)
  File ".../urllib3/request.py", line 88, in request_encode_url
    return self.urlopen(method, url, **urlopen_kw)
  File ".../urllib3/poolmanager.py", line 145, in urlopen
    conn = self.connection_from_host(u.host, port=u.port, scheme=u.scheme)
  File ".../urllib3/poolmanager.py", line 119, in connection_from_host
    pool = self._new_pool(scheme, host, port)
  File ".../urllib3/poolmanager.py", line 86, in _new_pool
    return pool_cls(host, port, **kwargs)
  File ".../urllib3/connectionpool.py", line 226, in __init__
    ConnectionPool.__init__(self, host, port)
  File ".../urllib3/connectionpool.py", line 156, in __init__
    host = host.strip('[]')
AttributeError: 'NoneType' object has no attribute 'strip'

Minimal Reproduction

repro.py

>> import urllib3
>> http = urllib3.PoolManager()
>> r = http.request('GET', 'http://@')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../urllib3/request.py", line 75, in request
    **urlopen_kw)
  File ".../urllib3/request.py", line 88, in request_encode_url
    return self.urlopen(method, url, **urlopen_kw)
  File ".../urllib3/poolmanager.py", line 145, in urlopen
    conn = self.connection_from_host(u.host, port=u.port, scheme=u.scheme)
  File ".../urllib3/poolmanager.py", line 119, in connection_from_host
    pool = self._new_pool(scheme, host, port)
  File ".../urllib3/poolmanager.py", line 86, in _new_pool
    return pool_cls(host, port, **kwargs)
  File ".../urllib3/connectionpool.py", line 226, in __init__
    ConnectionPool.__init__(self, host, port)
  File ".../urllib3/connectionpool.py", line 156, in __init__
    host = host.strip('[]')
AttributeError: 'NoneType' object has no attribute 'strip'

What Broke

Requests to malformed URLs result in AttributeError, causing application crashes.

Why It Broke

The connection_from_host method assumes host will never be None, leading to an AttributeError

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 the application relies on None being a valid host.

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/357

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 the application relies on None being a valid host.

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

Version	Status
1.25	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.

urllib3 "AttributeError: 'NoneType' object has no attribute 'strip'" with malformed URL (Fix)