Capture Additional Exception Attributes in traceback.TracebackException

[ericsnowcurrently]

Feature or enhancement

traceback.TracebackException currently captures all the information common to all exceptions. It also captures some of the information that is specific to certain builtin exceptions, enough to print all exceptions.

I don't have a motivating use case. My interest here is mostly conceptual. I think of TracebackException as a summary or representative proxy of an exception and currently there are gaps in that representation. If TracebackException is really only intended for printing exceptions/tracebacks then there probably isn't much to do here (and I'm okay with that). That said, I'll proceed here with my thoughts.

There are two categories of gap-in-representation that I see:

• some builtin exceptions aren't represented fully (e.g. ImportError)
• custom information for user-defined exception types aren't represented at all

Ultimately, it should probably be each exception type that determines what information should be preserved in a snapshot like TracebackException. That suggests room for a new protocol (i.e. "dunder" method). At the very least it would be nice to rely on exc.args, which all exceptions have, and map that to names. For non-builtin exceptions I don't see a real alternative to a general protocol.

For builtin exceptions, however, we can fill in the gaps in TracebackException manually, following the pattern of what we've done for SyntaxError and ExceptionGroup.

• ImportError
  • msg
  • name
  • path
  • name_from
• OSError
  • errno
  • winerror
  • strerror
  • filename
  • filename2
• SystemExit
  • code
• UnicodeError
  • encoding
  • reason
  • object
  • start
  • end
• BlockingIOError
  • characters_written
• BaseExceptionGroup
  • message
• StopIteration
  • value
• NameError
  • name
• AttributeError
  • name
  • obj
• SyntaxError
  • print_file_and_line

Related:

• Missing Signature Info for Builtin Exceptions in help() and Docs #111405
• traceback: add a new thin class storing a traceback without storing local variables #62111
• The Attributes of Exception Objects are not Clearly Documented and Easily Discoverable #111917
• Support Exception-like Objects (TracebackException) For exc.__cause__ and exc.__context__ #111921

[ericsnowcurrently]

On reflection, TracebackException isn't meant to be an actual snapshot of an exception. Rather, it's main purpose is to facilitate error display. Thus, it only needs to preserve information that affects how the exception is formatted, and it does not need these extra attributes.