[pypy-dev] feedback on PEP 421

[Laura Creighton]

In a message of Sun, 06 May 2012 21:29:12 +0200, Armin Rigo writes:
>The reason for that: getting details "right" might be similar to the
>sys module's documentation, which has grown a number of "CPython
>implementation detail" boxes --- which are rather meaningless for
>PyPy, in the sense that the set of functions that are dubbed "CPython
>implementation detail" and the set of functions that PyPy cannot
>reasonably implement have little to do with each other.

I think a large part of this problem is that CPython implementors are
completely unaware of what set of functions PyPy cannot implement.  
And I don't blame them for that.  I am often in the same way.  I talk
to somebody who wants to make CPython do X, and he wants to know if
PyPy will have a problem with this.  I cautiously reply 'not as
he has outlined the problem'.  3 weeks later, he comes back with
working code.  And I say -- Eeek! we cannot do this, that and the
other thing, and by the way we have a much more efficient way to do this
thing over there.  He quite reasonably asks me 'why didn't you tell
me this in the first place?' and I also reasonably reply 'I had no
idea that you planned this particular implementation when you asked.'

Is there a place in this PEP for 'known differences in implementations'
a.k.a. 'we know this is incompatible but we aren't going to change our 
implementation to fix'??  It might save a lot of trouble.

Laura