[Python-Dev] buffer interface (again)

[Guido van Rossum]

> I would like to use (again) the buffer interface,
> and I have some suggestions/questions.
> 
> - Only extension types can implement the buffer interface,
> no way for a python class. Maybe a magic method __buffer__(self)
> could be invented for this purpose?

How could it be made safe?  The buffer interface makes raw memory
addresses available.  Letting a Python class decide on what addresses
to use opens a big hole for abuse.

> - Why does the builtin function buffer() always return
> readonly buffers, even for read/write objects? Shouldn't
> there also be a readwrite_buffer() function, or should
> buffer() return read/write buffers for read/write objects?

It's a lifetime issue.  You can hold on to the object returned by
buffer() long after the actual memory it points to is recycled for
some other purpose, and while *reading* that memory is not such a big
deal (assuming it is still part of your address space, you'll just get
garbage), allowing it to be *written* is again an invitation to
disaster.

> - My bug report 216405 on sourceforge is still open
> (well, it is marked as closed, but it went into PEP 42)
> http://sourceforge.net/tracker/index.php?func=detail&aid=216405&group_id=5470&atid=105470

I still feel that your bug report is based on the wrong assumption
about what the buffer API should do.

Thomas, please first explain what you want to *do* with the buffer
interface.  Some of the buffer API was a mistake.  It *appears* to be
an interface for allocating and managing buffers, while in actuality
it is only intended to provide access to buffered data that is managed
by some C code.  You're probably better off using the array module to
manage buffers.

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