Hi,
Thanks for taking the time to consider the PEP.
Although the PEP was rejected, I still believe that the safety
guarantees in PEP 651 are worth adding to Python in the future.
To do that (maybe for 3.11), I need to understand your concerns better.
Would you clarify a few points for me?
On 03/03/2021 7:19 pm, Python Steering Council wrote:
Hi Mark,
Thank you for submitting PEP 651. The Steering Council has spent the past two
weeks reviewing PEP 651. After careful consideration, we have decided to reject
the PEP. The following were the key points that led us to this decision:
* The benefits are not compelling enough. Deep recursion is not a common tool in
Python, and even with PEP 651 it would not be efficient enough to make it a
common
tool.
* The benefit of PEP 651 is negated as soon as a non-Python function is
involved in the
recursion, making the likelihood of it being useful even smaller. It also
creates
easy pitfalls for users who do end up relying on recursion.
Could you give an example pitfall?
* We believe the PEP understates the disruption created by the technical
solution of
multiple Python stack frames per C call. Although this may be solvable, it
will
certainly cause substantial disruption to existing debuggers, tracers, and
state
inspection tools as they need to adapt to this change (which may not be
trivial).
This is presumably the key objection.
Is there a particular tool that you feel would be problematic?
I have only looked at gdb and py-spy.
* As the way to approach this will be platform-specific (as some parts of the
proposal
are not portable), this can cause generic Python code to behave differently
on
different platforms, making this kind of code less portable and less
predictable.
There are two issues here. Portability and changes to behaviour.
Regarding portability, I have to admit that PEP is rather vague.
That's my fault; I should have done more implementation first :(
FWIW, I have an implementation that should be portable.
https://github.com/python/cpython/compare/master...markshannon:pep-overflow-implementation
Regarding changes to behaviour, I don't see how "generic" Python code
would behave differently on different platforms, except for cases where
it already does.
In some cases, the PEP would have improved the situation.
For example:
sys.setrecursionlimit(5000)
def f():
f()
Currently, it raises a RecursionError on linux, but crashes the
interpreter on Windows.
With PEP 651 it would have raised a RecursionError on both platforms.
Am I missing something here?
Cheers,
Mark.
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