On 10/10/2018 00:06, Steven D'Aprano wrote:

On Tue, Oct 09, 2018 at 09:37:48AM -0700, Jeff Hardy wrote:

...

From an alternative implementation point of view, CPython's behaviour
*is* the spec. Practicality beats purity and all that.

Are you speaking on behalf of all authors of alternate implementations, 
or even of some of them?

It certainly is not true that CPython's behaviour "is" the spec. PyPy 
keeps a list of CPython behaviour they don't match, either because they 
choose not to for other reasons, or because they believe that the 
CPython behaviour is buggy. I daresay IronPython and Jython have 
similar.

While agreeing with the principle, unless it is one of the fundamental differences (GC, GIL), Jython usually lets practicality beat purity. When faced with a certain combination of objects, one has to do something, and it is least surprising to do what CPython does. It's also easier than keeping a record.

Rarely, we manage to exceed CPython (in consistency or coverage) by a tiny amount.

Jeff Allen