[Python-Dev] PEP 298, __buffer__

[Guido van Rossum]

> Scott Gilbert wrote:
> 
> >Tonight, I remember another thought that I've had for a while.
> >
> >There isn't currently a way for a class object created from Python script
> >to indicate that it wishes to implement the buffer interface.  In the
> >Numeric source, I've seen them use self.__buffer__ for this purpose, but
> >this isn't actually an officially sanctioned magic name.
> >
> >
> >I'm thinking one of:
> >
> >    class OneWay(object):
> >        def __init__(self):
> >            self.__buffer__ = bytes(1000)
> >
> >Or:
> >
> >    class SomeOther(object):
> >        def __init__(self):
> >            self._private = bytes(1000)
> >        def __buffer__(self):
> >            return self._private
> > 
> >I believe the first one is the way it's done in Numeric (Numarray too?). 

[Todd Miller]
> The numarray C-API essentially supports both usages, although we only 
> use the __buffer__ name in the second case.  
> 
> >
> >(Maybe Todd Miller will comment on this and whether it's useful to him.)
> >
> Yes, it is useful for prototyping.   Numarray calls a  __buffer__() 
> method to support python class wrappers around mmap.   We use our class 
> wrappers around mmap to add the ability to chop a file up into 
> non-overlapping resizeable slices.  Each slice can be used as the buffer 
> of an independent memory mapped array.

This would be easy enough to add, I suppose, but (a) I don't think
it's got much to do with PEP 298, and (b) let's wait until we have a
real use case, so perhaps we can decide which form it should take.
Until then, I call YAGNI.

--Guido van Rossum (home page: http://www.python.org/~guido/)