Here is a new version of the patch. The annotation is done on the code object instead of on the frame object. This avoids two problems: There is no runtime overhead, as the decorator returns the original function and no additional frames show up in the traceback. Since the variables are only known at runtime, the annotation is now a function that does the formatting of the annotation message and gets passed the frame object. With this there is no runtime overhead when no exception is raised and even if an exception is raise, but the traceback is never formatted.