Requests PreparedRequest check: use duck typing? (Fix)

The Fix

pip install requests==2.27.0

Based on closed psf/requests issue #3102 · 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

@@ -557,7 +557,7 @@ def send(self, request, **kwargs):
         # It's possible that users might accidentally send a Request object.
         # Guard against that specific failure case.
-        if not isinstance(request, PreparedRequest):
+        if isinstance(request, Request):
             raise ValueError('You can only send PreparedRequests.')

repro.py

Traceback (most recent call last):
  File "deploy.py", line 43, in <module>
    main(args.realm)
  File "deploy.py", line 29, in main
    results = [client.update_function_code(FunctionName=arn, ZipFile=data) for arn in arns]
  File "/home/ubuntu/webhooks/src/botocore/botocore/client.py", line 236, in _api_call
    return self._make_api_call(operation_name, kwargs)
  File "/home/ubuntu/webhooks/src/botocore/botocore/client.py", line 489, in _make_api_call
    operation_model, request_dict)
  File "/home/ubuntu/webhooks/src/botocore/endpoint.py", line 117, in make_request
    return self._send_request(request_dict, operation_model)
  File "/home/ubuntu/webhooks/src/botocore/endpoint.py", line 146, in _send_request
    success_response, exception):
  File "/home/ubuntu/webhooks/src/botocore/endpoint.py", line 219, in _needs_retry
    caught_exception=caught_exception)
  File "/home/ubuntu/webhooks/src/botocore/botocore/hooks.py", line 226, in emit
    return self._emit(event_name, kwargs)
  File "/home/ubuntu/webhooks/src/botocore/botocore/hooks.py", line 209, in _emit
    response = handler(**kwargs)
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 183, in __call__
    if self._checker(attempts, response, caught_exception):
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 250, in __call__
    caught_exception)
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 265, in _should_retry
    return self._checker(attempt_number, response, caught_exception)
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 313, in __call__
    caught_exception)
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 222, in __call__
    return self._check_caught_exception(attempt_number, caught_exception)
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 355, in _check_caught_exception
    raise caught_exception
ValueError: You can only send PreparedRequests.

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 requests==2.27.0\nWhen NOT to use: This fix is not safe if the library versions are not properly managed to avoid namespace conflicts.\n\n

Why This Fix Works in Production

Trigger: main(args.realm)
Mechanism: The check for PreparedRequest instances failed due to namespace conflicts from multiple library versions
Why the fix works: Flips the conditional check in session.send() to allow sending PreparedRequests created from different instances of the Requests library. (first fixed release: 2.27.0).

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 check for PreparedRequest instances failed due to namespace conflicts from multiple library versions
Surfaces as: Traceback (most recent call last):

Proof / Evidence

GitHub issue: #3102
Fix PR: https://github.com/psf/requests/pull/3108
First fixed release: 2.27.0
Reproduced locally: No (not executed)
Last verified: 2026-02-07
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.27

Discussion

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

Jump to Sources Open on GitHub

“That's a good question”

@Lukasa · 2016-04-18 · source

Failure Signature (Search String)

main(args.realm)

Error Message

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "deploy.py", line 43, in <module>
    main(args.realm)
  File "deploy.py", line 29, in main
    results = [client.update_function_code(FunctionName=arn, ZipFile=data) for arn in arns]
  File "/home/ubuntu/webhooks/src/botocore/botocore/client.py", line 236, in _api_call
    return self._make_api_call(operation_name, kwargs)
  File "/home/ubuntu/webhooks/src/botocore/botocore/client.py", line 489, in _make_api_call
    operation_model, request_dict)
  File "/home/ubuntu/webhooks/src/botocore/endpoint.py", line 117, in make_request
    return self._send_request(request_dict, operation_model)
  File "/home/ubuntu/webhooks/src/botocore/endpoint.py", line 146, in _send_request
    success_response, exception):
  File "/home/ubuntu/webhooks/src/botocore/endpoint.py", line 219, in _needs_retry
    caught_exception=caught_exception)
  File "/home/ubuntu/webhooks/src/botocore/botocore/hooks.py", line 226, in emit
    return self._emit(event_name, kwargs)
  File "/home/ubuntu/webhooks/src/botocore/botocore/hooks.py", line 209, in _emit
    response = handler(**kwargs)
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 183, in __call__
    if self._checker(attempts, response, caught_exception):
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 250, in __call__
    caught_exception)
  File "/home/ubu
... (truncated) ...

Minimal Reproduction

repro.py

Traceback (most recent call last):
  File "deploy.py", line 43, in <module>
    main(args.realm)
  File "deploy.py", line 29, in main
    results = [client.update_function_code(FunctionName=arn, ZipFile=data) for arn in arns]
  File "/home/ubuntu/webhooks/src/botocore/botocore/client.py", line 236, in _api_call
    return self._make_api_call(operation_name, kwargs)
  File "/home/ubuntu/webhooks/src/botocore/botocore/client.py", line 489, in _make_api_call
    operation_model, request_dict)
  File "/home/ubuntu/webhooks/src/botocore/endpoint.py", line 117, in make_request
    return self._send_request(request_dict, operation_model)
  File "/home/ubuntu/webhooks/src/botocore/endpoint.py", line 146, in _send_request
    success_response, exception):
  File "/home/ubuntu/webhooks/src/botocore/endpoint.py", line 219, in _needs_retry
    caught_exception=caught_exception)
  File "/home/ubuntu/webhooks/src/botocore/botocore/hooks.py", line 226, in emit
    return self._emit(event_name, kwargs)
  File "/home/ubuntu/webhooks/src/botocore/botocore/hooks.py", line 209, in _emit
    response = handler(**kwargs)
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 183, in __call__
    if self._checker(attempts, response, caught_exception):
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 250, in __call__
    caught_exception)
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 265, in _should_retry
    return self._checker(attempt_number, response, caught_exception)
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 313, in __call__
    caught_exception)
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 222, in __call__
    return self._check_caught_exception(attempt_number, caught_exception)
  File "/home/ubuntu/webhooks/src/botocore/botocore/retryhandler.py", line 355, in _check_caught_exception
    raise caught_exception
ValueError: You can only send PreparedRequests.

What Broke

Deployments to AWS failed with ValueError due to incompatible PreparedRequest instances.

Why It Broke

The check for PreparedRequest instances failed due to namespace conflicts from multiple library versions

Fix Options (Details)

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

pip install requests==2.27.0

When NOT to use: This fix is not safe if the library versions are not properly managed to avoid namespace conflicts.

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

Fix reference: https://github.com/psf/requests/pull/3108

First fixed release: 2.27.0

Last verified: 2026-02-07. Validate in your environment.

When NOT to Use This Fix

This fix is not safe if the library versions are not properly managed to avoid namespace conflicts.

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
2.27.0	Fixed

Related Issues

No related fixes found.

Cluster: requests:configuration-error Requests hub Requests best practices All hubs All clusters

Related clusters: Data consistency SSL handshake Other

Sources

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