[PyKDE] Panel applets with PyKDE/Python

Jim Bublitz jbublitz at nwinternet.com
Tue Aug 19 03:11:01 BST 2003

On Monday August 18 2003 16:06, Roland Schulz wrote:
> do you think the same would work for Custom Widgets in
> QtDesigner?

I just looked at Qt Designer quickly and I'm not real familiar 
with it.  I think what you're asking is "Would it be possible to 
create a custom widget in Python and have Qt Designer handle it 
properly?" , or am I missing the point?

Assuming that's what you're asking, the code would be different - 
this is very panel applet specific - but the basic approach 
should be the same. I'm also assuming that the "plugin.h" stuff 
in the custom widget section of the Qt Designer manual is 
methods that Qt Desinger calls that reside in the custom widget.
If that's also correct, then my guess is you'd have to do the 
same thing that PyKDE would do for panel applets, but once for 
each method.

For panel applets, kicker finds a .desktop file in its directory 
and from there gets the name of the panel applet .so lib to 
load. PyKDE will substitute a single .so that loads any Python 
panel applet (so it needs a mod to KDE/kicker to pass in the 
name of the script being requested - this is really easy to do).

Here's the part that I think is similar to Qt Designer: when 
kicker loads the lib for the applet, it looks for a function:

    KPanelApplet *init (QWidget *parent, QString& configFile);

(PyKDE's .so lib wants to see a script name in configFile, which 
doesn't happen right now).

A C++ applet's init would construct a KPanelApplet subclass that 
does whatever the applet's supposed to do and return a pointer 
to the subclass to kicker. Instead of that, PyKDE's init:

1. Loads the Python interpreter (from another linked .so lib)
2. Converts the QWidget and QString to PyObjects (using sip 
conversion functions from PyQt)
3. Loads the Python script into the interpreter
4. Calls a Python version of "init" in the script loaded (passes 
the args that kicker sent to init)., which then uses Python to 
construct the applet and returns a PyObject to the C++ init 
5. Converts (using sip again and PyKDE) the PyObject returned to 
a C++ KPanelApplet * and returns it to kicker.

It's taken more lines to describe it than to code it. Basically, 
you'd need to do the same thing with Qt Designer for each method 
(again if I understand it correctly after a quick look). 
Somebody who understands Qt plugins might have a better 

In fewer words, you need to provide a wrapper for the entire 
interface, and embed Python into it.

The two hard parts are:

1. Converting objects between C++ and Python domains - 
sip/PyQt/PyKDE make this easy.

2. Loading and comminicating with the Python interpreter - I 
built a lib that makes this easy too.

The problem with releasing this that the panel applet part is 
easier if tightly integrated into PyKDE, but I don't want to do 
that until KDE/kicker supports it. It's a lot of picky details 
to get this to build and link automatically (and that's true 
whether it's part of PyKDE or not). The python lib part is 
pretty stand-alone (it's independent of sip/PyKDE) - it's in 
C++, it has a complete set of unit tests (yay!) and I threw 
together a C wrapper (with it's own set of tests) in about 15 
minutes while waiting for FedEx to call for my pickup. If 
someone wants to see that, I can throw together some docs and 
tar it up. The only thing I don't know is if it's thread safe (I 
know NOTHING about threads).


> Am Montag, 18. August 2003 07:26 schrieb Jim Bublitz:
> > I've been promising to do something with this for quite a
> > while and finally got to it.

> > I spent some time this weekend playing around with the
> > possibility of writing panel applets for KDE (kicker) in
> > Python using PyKDE. David Boddie has made some preliminary
> > code available which I stole from shamelessly and with
> > mostly a little reorganization got it somewhat working.

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