On Wed, Oct 3, 2018 at 6:49 PM Anders Hovmöller <bo...@killingar.net> wrote:
>
> I don't really think accidents of implementation are different from hard
> requirements in Python, as it applies to alternative implementations. In
> practice if it deviates from CPython then it's broken. There is no language
> spec, there is only CPython. This has been the experience and approach of
> PyPy as far as I've understood it after having followed their blog over the
> years.
>
Definitely not true. There have been times when other implementors
have come to python-dev and said, hey, is this part of the spec or is
it an implementation detail? And the answer determines whether they
care about that or not. For just a few examples:
1) Reference counting vs nondeterministic garbage collection
2) O(1) indexing/slicing of Unicode strings
3) "\N{...}" string escapes (okay, that's standardized, but optional)
4) Reuse of id() values
5) The "slots" mechanism for dunder method lookup
The language spec determines, in some cases, that a CPython
implementation detail has been promoted to standard. More often, it
determines that other Pythons are permitted to behave differently.
ChrisA
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