Simon Willison • 12/9/2025

Deprecations via warnings don’t work for Python libraries

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The article discusses the failure of DeprecationWarning as a tool for API deprecation in Python libraries, using the recent urllib3 2.6.0 release as a case study. It explains how major downstream projects missed the warnings, forcing a rollback, and explores alternative practices like running test suites with `-Wonce::DeprecationWarning`.

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#Python #api #versioning
Deprecations via warnings don’t work for Python libraries

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