Development/Tutorials/Plasma4/Python/Writing DataEngines: Difference between revisions

    From KDE TechBase
    (Reword, add section)
    (Building blocks for the tutorial)
    Line 32: Line 32:


    == Main script ==
    == Main script ==
    For this tutorial we'll use the <tt>plasma-dataengine-pytime</tt> code, which is available on KDE's SVN. This DataEngine is an equivalent to the C++ time DataEngine we connected to in the [[../Using DataEngines|using DataEngines tutorial]]. Its function is to display time and date with respect to the current timezone. You can view [http://websvn.kde.org/branches/KDE/4.2/kdebase/workspace/plasma/scriptengines/python/examples/dataengines/pytime/contents/code/main.py?revision=906699&view=markup the main.py file online]. As the file is rather long, we'll take a look at it in sections.
    <code python>
    # Copyright stuff
    from PyQt4.QtCore import *
    from PyKDE4.kdecore import *
    from PyKDE4 import plasmascript
    class PyTimeEngine(plasmascript.DataEngine):
        def __init__(self,parent,args=None):
            plasmascript.DataEngine.__init__(self,parent)
        def init(self):
            self.setMinimumPollingInterval(333)
    </code>
    We start with the copyright information, followed by importing the required modules (<tt>PyQt4.QtCore</tt> and <tt>plasmascript</tt>). Since we're dealing with time and timezones, we also import <tt>kdecore</tt> to make use of what KDE offers.
    In <tt>__init__</tt> we just initialize the class. In <tt>init()</tt> instead, we set the minimum polling interval, that is  the minimum time (in milliseconds) that needs to pass between one data request (from an applet, for example) and another.
    <code python>
    def sources(self):
            sources = ["Local"]
            sources.extend(KSystemTimeZones.zones().keys())
            return sources
        def sourceRequestEvent(self, name):
            return self.updateSourceEvent(name)
    </code>

    Revision as of 08:59, 24 January 2009

    Abstract

    As you have seen in the using DataEngines tutorial, Plasma applets can make use of DataEngines to visualize data of many different kinds. In fact, the already available DataEngines offer many options for your applets. But what if you have a specific need, not covered by those?

    The problem is easily solved by writing your own Plasma DataEngine, and this tutorial will show you how to create one.

    Prerequisites

    As with applets, DataEngines need the same directory structure (see the Getting Started tutorial), so the first step is to create the appropriate directories. The difference with respect to applets lies in the metadata.desktop file:

    [Desktop Entry] Name=Python Date and Time Comment=Python Time data for Plasmoids Type=Service Icon=preferences-system-time ServiceTypes=Plasma/DataEngine X-Plasma-API=python

    X-KDE-PluginInfo-Author=Simon Edwards [email protected] X-KDE-PluginInfo-Name=plasma-dataengine-pytime X-KDE-PluginInfo-Version=1.0 X-KDE-PluginInfo-Website=http://plasma.kde.org/ X-KDE-PluginInfo-Category=Python Date and Time X-KDE-PluginInfo-Depends= X-KDE-PluginInfo-License=LGPL X-KDE-PluginInfo-EnabledByDefault=true

    Take a look at the ServiceType line. When using applets, it was "Plasma/Applet", but since now we're dealing with DataEngines, its value is "Plasma/DataEngine".

    Main script

    For this tutorial we'll use the plasma-dataengine-pytime code, which is available on KDE's SVN. This DataEngine is an equivalent to the C++ time DataEngine we connected to in the using DataEngines tutorial. Its function is to display time and date with respect to the current timezone. You can view the main.py file online. As the file is rather long, we'll take a look at it in sections.

    1. Copyright stuff

    from PyQt4.QtCore import * from PyKDE4.kdecore import * from PyKDE4 import plasmascript

    class PyTimeEngine(plasmascript.DataEngine):

       def __init__(self,parent,args=None):
           plasmascript.DataEngine.__init__(self,parent)
    
       def init(self):
           self.setMinimumPollingInterval(333)
    

    We start with the copyright information, followed by importing the required modules (PyQt4.QtCore and plasmascript). Since we're dealing with time and timezones, we also import kdecore to make use of what KDE offers.

    In __init__ we just initialize the class. In init() instead, we set the minimum polling interval, that is the minimum time (in milliseconds) that needs to pass between one data request (from an applet, for example) and another.

    def sources(self):

           sources = ["Local"]
           sources.extend(KSystemTimeZones.zones().keys())
           return sources
    
       def sourceRequestEvent(self, name):
           return self.updateSourceEvent(name)