Languages/Python/PyKDE 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.