On Thu, 6 Jan 2005 21:28:26 +1100, Anthony Baxter
<[EMAIL PROTECTED]> wrote:
> My take on this:
>
> struct.pack/struct.unpack is already one of my least-favourite parts
> of the stdlib. Of the modules I use regularly, I pretty much only ever
> have to go back and re-read the struct (and re) documentation because
> they just won't fit in my brain. Adding additional complexity to them
> seems like a net loss to me.
Have you looked at Thomas Heller's ctypes? Ignoring the FFI stuff, it
has a fairly comprehensive interface for defining and using C
structure types. A simple example:
>>> class POINT(Structure):
... _fields_ = [('x', c_int), ('y', c_int)]
...
>>> p = POINT(1,2)
>>> p.x, p.y
(1, 2)
>>> str(buffer(p))
'\x01\x00\x00\x00\x02\x00\x00\x00'
To convert *from* a byte string is messier, but not too bad:
>>> s = str(buffer(p))
>>> s
'\x01\x00\x00\x00\x02\x00\x00\x00'
>>> p2 = POINT()
>>> ctypes.memmove(p2, s, ctypes.sizeof(POINT))
14688904
>>> p2.x, p2.y
(1, 2)
It might even be possible to get Thomas to add a small helper
classmethod to ctypes types, something like
POINT.unpack(str, offset=0, length=None)
which does the equivalent of
def unpack(cls, str, offset=0, length=None):
if length is None:
length=sizeof(cls)
b = buffer(str, offset, length)
new = cls()
ctypes.memmove(new, b, length)
return new
> I'd _love_ to find the time to write a sane replacement for struct - as
> well as the current use case, I'd also like it to handle things like
> attribute-length-value 3-tuples nicely (where you get a fixed field
> which identifies the attribute, a fixed field which specifies the value
> length, and a value of 'length' bytes). Almost all sane network protocols
> (i.e. those written before the plague of pointy brackets) use this in
> some way.
I'm not sure ctypes handles that, mainly because I don't think C does
(without the usual trick of defining the last field as fixed length)
Paul.
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