[Python-Dev] marshal (was:Buffer interface in abstract.c? )

[Greg Stein]

Fredrik Lundh wrote:
> 
> > > > >>> import unicode
> > > > >>> import marshal
> > > > >>> u = unicode.unicode
> > > > >>> s = u("foo")
> > > > >>> data = marshal.dumps(s)
> > > > >>> marshal.loads(data)
> > > > 'f\000o\000o\000'
> > > > >>> type(marshal.loads(data))
> > > > <type 'string'>

This was a "nicety" that was put during a round of patches that I
submitted to Guido. We both had questions about it but figured that it
couldn't hurt since it at least let some things be marshalled out that
couldn't be marshalled before.

I would suggest backing out the marshalling of buffer-interface objects
and adding a mechanism for arbitrary type objects to marshal themselves.
Without the second part, arrays and Unicode objects aren't marshallable
at all (seems bad).

> > Why do Unicode objects implement the bf_getcharbuffer slot ? I thought
> > that unicode objects use a two-byte character representation.

Unicode objects should *not* implement the getcharbuffer slot. Only
read, write, and segcount.

> >>> import array
> >>> import marshal
> >>> a = array.array
> >>> s = a("f", [1, 2, 3])
> >>> data = marshal.dumps(s)
> >>> marshal.loads(data)
> '\000\000\200?\000\000\000@\000\000@@'
> 
> looks like the various implementors haven't
> really understood the intentions of whoever
> designed the buffer interface...

Arrays can/should support both the getreadbuffer and getcharbuffer
interface. The former: definitely. The latter: only if the contents are
byte-sized.

The loading back as a string is a different matter, as pointed out
above.

Cheers,
-g

--
Greg Stein, http://www.lyra.org/