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Title: gh-128384: Add thread-safe context manager to "warnings" module by nascheme · Pull Request #128300 · python/cpython · GitHub

Open Graph Title: gh-128384: Add thread-safe context manager to "warnings" module by nascheme · Pull Request #128300 · python/cpython

X Title: gh-128384: Add thread-safe context manager to "warnings" module by nascheme · Pull Request #128300 · python/cpython

Description: This PR adds a new thread-local (and async friendly) context manager that uses contextvars. The recommended pattern for new code that doesn't care about backwards compatibility would be: with warnings.local_context() as ctx: ctx.simplefilter(...) ... For code that wants to be compatible with older versions of Python, the suggested code is: import warnings try: warn_ctx = warnings.get_context except AttributeError: def warn_ctx(): return warnings with warn_ctx().catch_warnings(): warn_ctx().simplefilter(...) ... with warn_ctx().catch_warnings(record=True) as log: ... This change retains warnings.filters and warnings.catch_warnings() as mechanisms that use process global state. Conceptually, there will be two sets of warning filters: the legacy process global warnings.filters list and the thread local get_context()._filters list. The context object returned by get_context() has an API that overlaps with the warnings module function API. Perhaps we could eventually warn when the process global versions are used but I think that would be many years in the future and not worth considering now. It would be intuitive if the thread local filtering was inherited when a new thread is created. I've created a separate PR that adds this feature to threading.Thread: gh-128209. That's a potentially controversial change but I think it's the correct thing to do. It will make contextvars behave similarly between asyncio tasks (which already inherit context) and threads. I think people will expect the warnings context manager to have lexical scope. If you see the code: with warnings.local_context() as ctx: ctx.simplefilter(MyWarning) inner_function() Then you would assume that inner_function() is going to have MyWarning filtered, even if it internally spawns a thread. Regarding backwards compatibility, I did a code search and there are quite a few examples for code that manipulates warnings.filters directly, either mutating it or assigning a different list to the module global. There is also code that does this: warnings.simplefilter(...) ... warnings.filters.pop(0) 📚 Documentation preview 📚: https://cpython-previews--128300.org.readthedocs.build/ Issue: gh-128384

Open Graph Description: This PR adds a new thread-local (and async friendly) context manager that uses contextvars. The recommended pattern for new code that doesn't care about backwards compatibility would be: with ...

X Description: This PR adds a new thread-local (and async friendly) context manager that uses contextvars. The recommended pattern for new code that doesn't care about backwards compatibility would be: w...

Opengraph URL: https://github.com/python/cpython/pull/128300

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