[Python-Dev] Buffered streams design + raw io gotchas

[Guido van Rossum]

Not really, BufferedRandom is only suitable when the file is open for
reading *and* writing. The 'rb' and 'wb' modes should return
BufferedReader and BufferedWriter, respectively.

On Sat, Feb 20, 2010 at 6:20 AM, Pascal Chambon
<chambon.pascal at gmail.com> wrote:
>
> Allright, so in the case of regular files I may content myself of
> BufferedRandom.
> And maybe I'll put some warnings concerning the returning of raw streams by
> factory functions.
>
> Thanks,
>
> Regards,
> Pascal
>
>
> Guido van Rossum a écrit :
>
> IIRC here is the use case for buffered reader/writer vs. random: a
> disk file opened for reading and writing uses a random access buffer;
> but a TCP stream stream, while both writable and readable, should use
> separate read and write buffers. The reader and writer don't have to
> worry about reversing the I/O direction.
>
> But maybe I'm missing something about your question?
>
> --Guido
>
> On Thu, Feb 18, 2010 at 1:59 PM, Pascal Chambon
> <chambon.pascal at gmail.com> wrote:
>
>
> Hello,
>
> As I continue experimenting with advanced streams, I'm currently beginning
> an important modification of io's Buffered and Text streams (removal of
> locks, adding of methods...), to fit the optimization process of the whole
> library.
> However, I'm now wondering what the idea is behind the 3 main buffer classes
> : Bufferedwriter, Bufferedreader and Bufferedrandom.
>
> The i/o PEP claimed that the two first ones were for sequential streams
> only, and the latter for all kinds of seekable streams; but as it is
> implemented, actually the 3 classes can be returned by open() for seekable
> files.
>
> Am I missing some use case in which this distinction would be useful (for
> optimizations ?) ? Else, I guess I should just create a RSBufferedStream
> class which handles all kinds of situations, raising InsupportedOperation
> exceptions whenever needed.... after all, text streams act that way (there
> is no TextWriter or TextReader stream), and they seem fine.
>
> Also, io.open() might return a raw file stream when we set buffering=0. The
> problem is that raw file streams are NOT like buffered streams with a buffer
> limit of zero : raw streams might fail writing/reading all the data asked,
> without raising errors. I agree this case should be rare, but it might be a
> gotcha for people wanting direct control of the stream (eg. for locking
> purpose), but no silently incomplete read/write operation.
> Shouldn't we rather return a "write through" buffered stream in this case
> "buffering=0", to cleanly handle partial read/write ops ?
>
> regards,
> Pascal
>
> PS : if you have 3 minutes, I'd be very interested by your opinion on the
> "advanced modes" draft below.
> Does it seem intuitive to you ? In particular, shouldn't the "+" and "-"
> flags have the opposite meaning ?
> http://bytebucket.org/pchambon/python-rock-solid-tools/wiki/rsopen.html
>
>
>
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-- 
--Guido van Rossum (python.org/~guido)