[issue12857] Expose called function on frame object

[Nathaniel Smith]

Nathaniel Smith added the comment:

I'd also like to make use of this in trio, as a way to get safer and less complicated control-C handling without having to implement things in C. (Exhaustive discussion: https://vorpus.org/blog/control-c-handling-in-python-and-trio/)

@Nick: I understand your proposal is to add a field on the frame that for regular function calls points to the function object, and for generator/coroutines points to the generator/coroutine object. Is that right? Two possible concerns there: (a) this creates a reference cycle, because generator/coroutine objects own a reference to the frame object, (b) AFAICT you also currently can't get from a generator/coroutine object back to the function object, so this would break some (all?) of the use cases for this. I guess the solution to (a) is to make it a weak reference, and for (b) either keep f_func as always pointing to the function and make f_generator a separate field, or else make it f_origin and also add gi_func/co_func fields to generator/coroutine objects. (Which might be useful in any case.)

Also, I'm not quite following the proposed use case. When a generator/coroutine is resumed, then send() steps through the whole yield stack and reconstructs the frame stack so it matches the generator/coroutine stack. (throw() currently doesn't do this, but that's a bug that breaks profilers/debuggers/etc - bpo-29590 - so we should fix it anyway, and I think Yury is planning to do that soon.) So if you get a frame from sys._getframe() or similar, then the stack is correct. And if a coroutine/generator isn't running, then the only way to get to the frame is by starting with the coroutine/generator object, so we don't really need a way to get back.

Tracebacks are a different case again because they continue to hold frame references after the stack is unwound, but generally the traceback already has the correct stack because the exception propagates up the coroutine/generator stack, and also aren't the {gi,co}_frame references cleared as the exception propagates anyway?

----------
nosy: +njs

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue12857>
_______________________________________