[Python-Dev] Small question about BufferedRandom spec

[Guido van Rossum]

On Mon, Jan 5, 2009 at 12:01 PM, Antoine Pitrou <solipsis at pitrou.net> wrote:
> Amaury (mainly) and I are rewriting the IO stack in C,

Very cool!

> and there is a small
> thing in PEP 3116 about the BufferedRandom object that I'd like to clarify:
>
> « Q: Do we want to mandate in the specification that switching between reading
> and writing on a read-write object implies a .flush()? Or is that an
> implementation convenience that users should not rely on? »
>
> Is it ok if I assume that the answer is "it is an implementation convenience
> that users should not rely on"? The reason is that I'm overhauling
> BufferedRandom objects to use a single shared buffer, so as to optimize
> interleaved reads and writes.

I think it's fine if the flush to the file is optional, as long as
this is clearly documented. However, the semantics of interleaving
reads and writes, with and without seek calls in between, should be
well-defined and correct/useful, so that it behaves the same
regardless of the buffer size.

Ditto for the flush call currently implied by a seek -- if you can
satisfy the seek by moving where you are in the buffer without
flushing, that's fine IMO, but it should be well documented.

It should also be documented that a flush still *may* occur, of course.

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