Proper application of the buffer interface

[Mark Hammond]

About a week ago, I wrote in message
<006501bedeee$33ef5c20$1101a8c0 at bobcat>...

>Just to extend my guesswork somewhat, there is a new built-in "buffer()"
>function.  This returns a "buffer" object.  I speculate this should be used
>in preference to Python strings when you have binary data.  As this buffer
>object supports the buffer interfaces, they are basically as functional as
>strings for this purpose, but clearly indicate the data is not really a
>string!  This appears to be more a matter of style, and also paves the road
>to Unicode - eg, it makes sense to convert any Python string object to
>Unicode, but not necessarily a binary buffer.

Just to prove it was guess-work, Bill Tutt indirectly pointed me at my error
here.

I may have given the impression that the buffer object returns a completely
new object - similar to a string.  The reason I may have given that
impression is because it is exactly what I meant.  However, it is wrong (and
I did know it was wrong <sigh>)

The "buffer()" built-in returns a read-only buffer for an _existing_ object.
It would only be an effective replacement for a string as a "byte buffer"
when coupled with an array object.

>>> import array
>>> a=array.array("b", range(ord('A'), ord('G')))
>>> b=buffer(a)
>>> b
<read-only buffer for fdcca0, ptr fdcc90, size 6 at fdccd0>
>>> b[:-1]
'ABCDE'
>>>

Just thought it worth a clarification.

As a side note, this also makes it far more difficult for extensions to
replace the use of strings with a different object for "byte buffers" - it
appears PyArray_New does not exist, so extension module writers are forced
to implement their own object if they wish to use the buffer interface, but
not use a PyString.

Mark.