[Python-Dev] PEP 380

Michael Foord fuzzyman at voidspace.org.uk
Sat Nov 26 14:46:12 CET 2011

On 26/11/2011 07:46, Maciej Fijalkowski wrote:
> On Sat, Nov 26, 2011 at 6:39 AM, Nick Coghlan<ncoghlan at gmail.com>  wrote:
>> On Sat, Nov 26, 2011 at 8:14 AM, Michael Foord
>> <fuzzyman at voidspace.org.uk>  wrote:
>>> On 24 Nov 2011, at 04:06, Nick Coghlan wrote:
>>>> On Thu, Nov 24, 2011 at 10:28 AM, Guido van Rossum<guido at python.org>  wrote:
>>>>> Mea culpa for not keeping track, but what's the status of PEP 380? I
>>>>> really want this in Python 3.3!
>>>> There are two relevant tracker issues (both with me for the moment).
>>>> The main tracker issue for PEP 380 is here: http://bugs.python.org/issue11682
>>>> That's really just missing the doc updates - I haven't had a chance to
>>>> look at Zbyszek's latest offering on that front, but it shouldn't be
>>>> far off being complete (the *text* in his previous docs patch actually
>>>> seemed reasonable - I mainly objected to way it was organised).
>>>> However, the PEP 380 test suite updates have a dependency on a new dis
>>>> module feature that provides an iterator over a structured description
>>>> of bytecode instructions: http://bugs.python.org/issue11816
>>> Is it necessary to test parts of PEP 380 through bytecode structures rather than semantics? Those tests aren't going to be usable by other implementations.
>> The affected tests aren't testing the PEP 380 semantics, they're
>> specifically testing CPython's bytecode generation for yield from
>> expressions and disassembly of same. Just because they aren't of any
>> interest to other implementations doesn't mean *we* don't need them :)
>> There are plenty of behavioural tests to go along with the bytecode
>> specific ones, and those *will* be useful to other implementations.
>> Cheers,
>> Nick.
> I'm with nick on this one, seems like a very useful test, just
> remember to mark it as @impl_detail (or however the decorator is
> called).

Fair enough. :-)

If other tests are failing (the semantics are wrong) then having a test 
that shows you the semantics are screwed because the bytecode has been 
incorrectly generated will be a useful diagnostic tool.

On the other hand it is hard to see that bytecode generation could be 
"wrong" without it affecting some test of semantics that should also 
fail - so as tests in their own right the bytecode tests *must* be 
superfluous (or there is some aspect of the semantics that is *only* 
tested through the bytecode and that seems bad, particularly for other 

All the best,


> Cheers,
> fijal


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May you find forgiveness for yourself and forgive others
May you share freely, never taking more than you give.
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