Warnings

Make Warning Tests Concurrency-Safe with Context-Aware Warnings

Python’s warnings.catch_warnings() is convenient in tests, compatibility shims, and small diagnostic scopes. It lets code temporarily change warning filters and then restore the previous state. That model becomes harder to reason about when several threads or asynchronous tasks use it at the same time. Historically, catch_warnings() manipulated process-global state in the warnings module. Two overlapping contexts could therefore interfere with each other. Python 3.14 adds an opt-in context-aware mode that changes this behavior. When sys.flags.context_aware_warnings is true, catch_warnings() stores its filtering state in a context variable instead of mutating the same global warning state for every concurrent execution path.