Issue 43527: Support full stack trace extraction in warnings. (original) (raw)

When triggering warnings, it's possible to pass in a stacklevel in order to point to a more informative cause than the warnings.warn call.

For instance stacklevel=2 is a common one for DeprecationWarning in order to mark the call itself as deprecated in the caller's codebase.

The problem with this is that it's not transitive, so when a dependency triggers a warning it can be hard to know where that comes from in the codebase (at least without -Werror which can prevent reaching the interesting warning entirely), and whether this is an issue in the codebase (e.g. passing bytes where the library really works in terms of strings) or whether it would be possible to work around the warning by using some other API.

In that case, the ability to show a full stack trace from the stacklevel down is very useful to diagnose such issues.

Not quite sure how it would be managed though: I'd think this should be part of the warnings filter information, but the stacklevel currently isn't stored there, and it might be risky to extend the warnings filter with a 6th field).