On 8/16/2021 12:47 AM, Guido van Rossum wrote:
> My current proposal is to issue a DeprecationWarning in PyCode_New() and
> PyCode_NewWithPosArgs(), which can be turned into an error using a
> command-line flag. If it's made an error, we effectively have (B); by
> default, we have (A).
>
> Then in 3.13 we can drop them completely.
We definitely had legitimate use cases come up when adding positional
arguments (hence the new API, rather than breaking the existing one,
which was the first attempt at adding the feature).
I don't recall exactly what they are (perhaps Pablo does, or they may be
in email/issue archives), but since they exist, presumably they are
useful and viable _despite_ the bytecode varying between releases. This
suggests there's probably a better API we should add at the same time -
possibly some kind of unmarshalling or cloning-with-updates function?
I presume the use cases are essentially some variant of the .replace() API that exists at the Python level. At the C level you would get all fields from an existing code object and pass them to PyCode_New[WithPosArgs] except for e.g. the co_filename field. Unfortunately those use cases will still break if there are any try blocks in the code or if the endline/column info is needed. Also you can't access any of the code object's fields without the internal API (this wasn't always so). So I think it's different now.