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December 8, 2025

Deprecations via warnings don’t work for Python libraries

Last week urllib3 v2.6.0 was released which contained removals for several APIs that we've known were problematic since 2019 and have been deprecated since 2022. The deprecations were marked in the documentation, changelog, and what I incorrectly believed would be the most meaningful signal to users: with a DeprecationWarning being emitted for each use for the API.

This API was emitting warnings for over 3 years in a top-3 Python package by downloads urging libraries and users to stop using the API and that was not enough. So what should we do instead?

Read more: https://sethmlarson.dev/deprecations-via-warnings-dont-work-for-python-libraries

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