binary data through dbus-python

Tomeu Vizoso tomeu at
Thu Dec 21 07:45:52 PST 2006

Hi Simon,

we're gonna have 0.80 on the olpc, so that's what I'm targeting. I have
had partial success with your suggestions.

Sending a str, the other side receives a ByteArray (in a method with
byte_arrays=True with a parameter signature of 'ay'). That's good.

In another method I'm returning back this same object, using
out_signature='ay'. I verified that I'm sending a ByteArray, but the
other side receives an dbus.Array. I also tried byte_arrays=True.

Is there any way of receiving a str or ByteArray instead of an Array? If
not, what's the best way for converting this Array in a str (or



On Wed, 2006-12-20 at 22:03 +0000, Simon McVittie wrote:
> Hash: SHA1
> On Wed, 20 Dec 2006 at 22:16:41 +0100, Tomeu Vizoso wrote:
> > I need to pass some binary data (for images, audio, etc.) from python to
> > python through dbus using the latest dbus-python (this stuff is for the
> > olpc).
> > 
> > What is the recommended way for doing this? Which data types should I
> > use in the method signatures?
> Array of bytes, 'ay'. There are some more efficient paths in dbus-python 0.80
> for this purpose.
> > If the answer is to use an array of bytes, what is the best way to
> > convert an string to an array of bytes and back? iterating?
> Sending:
> If you're prepared to depend on dbus-python >= 0.80rc1 (actually
> 0.79.91 internally) and on the remote object's Introspect method working
> correctly, just pass a 'str' object where an array of bytes is
> expected, and dbus-python should do the right thing. If you need to
> support 0.71 or older, or you're calling a method on some object
> that doesn't support Introspect() correctly, or it's for a variant parameter,
> use dbus.ByteArray(my_str) to get a str subclass that dbus-python will
> understand to be a byte array, at the cost of an extra object allocation
> and an extra memcpy().
> Receiving:
> If you can rely on >= 0.80rc1, pass a keyword argument
> byte_arrays=True to the @method decorator, connect_to_signal or
> add_signal_receiver (as appropriate), or to the Message object's
> get_args_list method if you're using low-level API. You'll get a
> ByteArray back - it's a subclass of str, so it implements the read-only
> buffer interface that your imaging library probably uses.
> Currently, doing byte_array[i] on a ByteArray gives you a Byte (an
> int subclass) but I think I'm going to go back to it producing a str of
> length 1 before the final release of 0.80. You can always use
> str(my_byte_array) to get a real str object, again at a cost of one object
> allocation and one memcpy().
> If you need to support 0.71 or older, get the list of Byte objects and
> do ''.join(map(chr, my_list_of_bytes)) or
> ''.join([chr(x) for x in my_list_of_bytes]) or some such.
> We hope to release dbus-python 0.80 sometime in January.
> Regards,
> 	Simon
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