On 12/06/2017, Serhiy Storchaka <storchaka@gmail.com> wrote:
But if an error is raised when execute undo_something(), it replaces the original exception which become chaining as the __context__ attribute. The problem is that this can change the type of the exception. If do_something_other() raises SystemExit and undo_something() raises KeyError, the final exception has type KeyError.
For Python 2.7, I've used the following idiom, which always masks errors from the undo: do_something() try: do_something_other() except: try: undo_something() finally: raise Unfortunately, that breaks down on Python 3, as the new exception propogates with the original as context..
Does it mean that we should rewrite every chunk of code similar to the above? And if such cumbersome code is necessary and become common, maybe it needs syntax support in the language? Or changing the semantic of exceptions raised in error handlers and finally blocks?
What I want is a way to chain exceptions in the other direction, raising the original error, but attaching a related one. Unfortunately neither __cause__ or __context__ really help. Martin