(context)
Guido van Rossum schrieb am 13.08.21 um 19:24:
> In 3.11 we're changing a lot of details about code objects. Part of this is
> the "Faster CPython" work, part of it is other things (e.g. PEP 657 -- Fine
> Grained Error Locations in Tracebacks).
>
> As a result, the set of fields of the code object is changing. This is
> fine, the structure is part of the internal API anyway.
>
> But there's a problem with two public API functions, PyCode_New() and
> PyCode_NewWithPosArgs(). As we have them in the main (3.11) branch, their
> signatures are incompatible with previous versions, and they have to be
> since the set of values needed to create a code object is different. (The
> types.CodeType constructor signature is also changed, and so is its
> replace() method, but these aren't part of any stable API).
>
> Unfortunately, PyCode_New() and PyCode_NewWithPosArgs() are part of the PEP
> 387 stable ABI. What should we do?
>
> A. We could deprecate them, keep (restore) their old signatures, and create
> crippled code objects (no exception table, no endline/column tables,
> qualname defaults to name).
>
> B. We could deprecate them, restore the old signatures, and always raise an
> error when they are called.
>
> C. We could just delete them.
>
> D. We could keep them, with modified signatures, and to heck with ABI
> compatibility for these two.
>
> E. We could get rid of PyCode_NewWithPosArgs(), update PyCode() to add the
> posonlyargcount (which is the only difference between the two), and d*mn
> the torpedoes.
>
> F. Like (E), but keep PyCode_NewWithPosArgs() as an alias for PyCode_New()
> (and deprecate it).
>
> If these weren't part of the stable ABI, I'd choose (E). [...]
I also vote for (E). The creation of a code object is tied to interpreter
internals and thus shouldn't be (or have been) declared stable.
I think you're one of the few people who call those functions, and if even you think it's okay to break backward compatibility here, I think we should just talk to the SC to be absolved of having these two in the stable ABI. (Petr, do you agree? Without your backing I don't feel comfortable even asking for this.)
I think the only problem with that argument is that code objects are
required for frames. You could argue the same way about frames, but then it
becomes really tricky to, you know, create frames for non-Python code.
Note there's nothing in the stable ABI to create frames. There are only functions to *get* an existing frame, to inspect a frame, and to eval it. In any case even if there was a stable ABI function to create a frame from a code object, one could argue that it's sufficient to be able to get an existing code object from e.g. a function object.
Since we're discussing this in the context of PEP 657, I wonder if there's
a better way to create tracebacks from C code, other than creating fake
frames with fake code objects.
Cython uses code objects and frames for the following use cases:
- tracing generated C code at the Python syntax level
- profiling C-implemented functions
- tracebacks for C code
Having a way to do these three efficiently (i.e. with close to zero runtime
overhead) without having to reach into internals of the interpreter state,
code objects and frames, would be nice.
Failing that, I'm ok with declaring the relevant structs and C-API
functions non-stable and letting Cython use them as such, as we always did.
I think others have answered this already -- in any case it's not the immediate subject of this thread, and I don't have a strong opinion on it.