Languages/Python/PyKDE Knotify Tutorial

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Warning

This tutorial uses Qt4, PyQt4, and PyKDE4.

Python KNotify Tutorial

Tutorial Series	Python
Previous	None
What's Next
Further Reading	Qt Signals and Slots in python, Introduction to PyQT4, Using PyKDE4

Abstract

The aim of this tutorial is to give a sample class to include Notifications and Jobs to your own python programms, so the user can see what is going on (for example a backup system, that tells you that is backuping right now). It assumes a basic working knowledge of Python and PyKDE4. For now only the Job part is mentioned, 'cause that is the only part I've created right now.

Further plans

To add the Notification part also to this tutorial.

Instruction

We start with a minimal KDE Appliciation (Using PyKDE4):

#! /usr/bin/python
# -*- coding: utf-8 -*-

if __name__ == "__main__":
    import sys
    
    from PyKDE4.kdecore import KCmdLineArgs, KAboutData, KLocalizedString, ki18n
    from PyKDE4.kdeui import KApplication    
    
    appName     = "default"
    catalog     = ""
    programName = ki18n ("default")  
    version     = "1.0"
    description = ki18n ("Default Example")  
    license     = KAboutData.License_GPL
    copyright   = ki18n ("(c) 2010 Sandro Knauß") 
    text        = ki18n ("none") 
    homePage    = "techbase.kde.org"
    bugEmail    = "[email protected]"

    aboutData   = KAboutData (appName, catalog, programName, version, description,
                              license, copyright, text, homePage, bugEmail)

    
    KCmdLineArgs.init (sys.argv, aboutData)
    
    app = KApplication ()

Job class

The first step is to have a look to the [1]. The intersting on is:

• KJob(KDE 4.3-PyKDE4)- unfortunately this documention is only available for KDE 4.3. So we have also a look to the actual C++ Doumentation
• KJob(KJob 4.x-C++API)

So it is easy to write a small Job-Class:

from PyQt4.QtCore import QObject,QTimer,QString
from PyKDE4.kdecore import KJob

class MyJob(KJob):
    def __init__(self,parent=QObject()):
        KJob.__init__(self,parent)
        #We want to have a Suspenable and Killable Job
        self.setCapabilities(KJob.Capabilities(KJob.Suspendable|KJob.Killable))

        #Just a maximum Variable
        self.max=25

        #index
        self.i=0

    def start(self):
        #initalizing for work
        self.i=0
       
        #start the actual work in another thread
        #this function has to terminate, before the work is done
        QTimer().singleShot(0, self.doWork)
                                                                                                                                               
    def doWork(self):             
        #the actual work                                         
        try:            
            #if we are killed or suspended just return                                           
            if self.error() or self.isSuspended():                    
                return
        except RuntimeError:
            #if this class is killed before a RuntimeError will raise
            return

        #do a peace of hard work
        self.i+=1

        #fortunately we have made a peace of work 
        #-> show this to everybody
        KJob.setPercent(self,self.i*4)
       
        if self.i==self.max:
            #jeah we have done the bunch of work
            #send the result signal for showing, that we ended the work
            self.emitResult()
            return 
        #just go to sleep for 1000ms than go on
        QTimer().singleShot(1000, self.doWork)
    
    def doSuspend(self):
        #the surounding function from KJob makes the isSuspended() become True
        #returns True for signaling that this class supports to suspend
        return True

    def doResume(self):
        #start with work again
        QTimer().singleShot( 0, self.doWork )
        #return True for signaling that this class supports resuming
        return True

    def doKill(self):
        #return True for signaling that we support killing
        return True

What is going on?

• MyJob.__init__: First we create the class and initialize the counter i and the maximum max. To make is visible for others we set the Capacities, so this job is suspendable and killable.
• MyJob.start: Here the pre working setting are made, we will se later for what we use this. After initalizing the Work we start the actual work by using a QTimer. The start method should start the asyncron.
• MyJob.doWork: Do actual work and handle, if this job is killed or suspended.
• MyJob.doSuspend/MyJob.doResume/MyJob.doKill: These function indicate that this feature is supported by this class.

How to use?

Just create a instance of this class and start it:

job=MyJob(app)
job.start()

We want to know when the jobs done?

Create a SLOT to the result-signal:

def handleResult(job):
    #handleResult Function
    #it is called when the job is terminating
    if job.error():
       print 'error happend'
    else:
       print 'job has terminated successfully'
    
    #for terimation the complete application
    sys.exit()

job.result.connect(handleResult)

Now we also add app.exec_() at the end of the main part, to prevent the program to stop before the job is stopped.

Visual feedback

Till now, a normal user doesn't see anything what is going on. To change it we have to register the Job to a JobTracker. Now a user will see a progressbar and a suspend and a stop button. So we modify the start method:

from PyKDE4.kio import KIO
...
    def start(self):
        #register the Job to the JobTracker
        KIO.getJobTracker().registerJob(self)
        self.i=0
        QTimer().singleShot(0, self.doWork)

Setting the job title and description

Now you have the running job and a user can see nice progressbar. However, there is no visible information what job is currently running and what it is doing. To change it we have to emit signal KJob.description in our method MyJob.doWork:

    def doWork(self):             
        #the actual work                                         
        try:            
            #if we are killed or suspended just return                                           
            if self.error() or self.isSuspended():                    
                return
        except RuntimeError:
            #if this class is killed before a RuntimeError will raise
            return

        #do a peace of hard work
        self.i+=1

        #fortunately we have made a peace of work 
        #-> show this to everybody
        KJob.setPercent(self,self.i*4)
        self.description.emit(self, "Our Splendid Job", ("Source","counter"), ("Destination","dummy"))
       
        if self.i==self.max:
            #jeah we have done the bunch of work
            #send the result signal for showing, that we ended the work
            self.emitResult()
            return 
        #just go to sleep for 1000ms than go on
        QTimer().singleShot(1000, self.doWork)

The parameters of this signal are the sending job (anything else than self doesn't make sense here), job title, and two tuples consising of two strings arbitrary that can be used to denote some job details. (consider them as a key-value pair).

Conclusion

Here is the full code of this example.

Is is very easy to create a Job and make it visible to normal users.