1. Fedora Project / Red Hat
PyGTK for Beginners
Paul W. Frields
Fedora Project / Red Hat
Southeast LinuxFest
June 13, 2010
Very excited to be here
Thank the entire FOSSMeet team for their help in setting up this talk
The Fedora Project is proud to help sponsor this conference, spreading FOSS
A little about me:
* Worked with Linux for >10 years
* Joined Fedora Project in 2003 as a volunteer
* Inaugural Board member in 2006
* February – Red Hat full time as FPL
Copyright © 2010 Paul W. Frields, some rights reserved. Licensed under a Creative Commons Attribution-ShareAlike (CC BY-SA) 3.0 license.

2. What this talk covers
Tools you can use to build and understand a graphical user interface (GUI)
Understanding the GTK object and signal models
How to hook Python code to a GUI
Things to consider when designing your application (code and GUI)

3. What this talk does not cover
How to be a good programmer
The Python language
Intro for programmers: Mark Pilgrim's Dive Into Python
For absolute beginners: Wesley Chun's Core Python Programming
User experience, human-computer interaction

4. What this talk presumes
You know elementary programming concepts (variables, conditionals, loops, functions)
You've written Python or another scripting language but you're not a programmer
You are using a Linux system, not necessarily Fedora

5. Things you need
Python
GTK
Text editor of choice

6. Things you'll want
Glade3
Devhelp

7. Installing the tools
Fedora, openSUSE: Use Add/Remove Software tool to add the GNOME Software Development collection
Ubuntu: Use Synaptic Package Manager tool to add the python-gtk2-dev and glade packages

8. Workflow Glade to design UI (as GtkBuilder) Saved as XML
Can be tweaked in Glade or any editor
Python code loads the XML file as a resource
Interactive elements assigned to objects
Functions called based on interaction

9. GTK object model Based on classes and inheritance
Each object can have its own special properties and methods
Real-life example: “Chair” object, has a location property
FoldingChair adds fold( ) function
SwivelChair adds rotate( ) function

10. GTK object hierarchy example
GtkButton: pushbutton widget, subclass of...
GtkBin: widget that contains only one widget, subclass of...
GtkContainer: widget that's a container for other widgets, subclass of...
GtkWidget: object that is the base for all widgets, subclass of...
GtkObject: base for all objects

11. How to learn more
This is where devhelp comes in – provides hierarchical listing of inheritance
For example, let's look at GtkButton in the listing
Note that GtkButton inherits the properties and methods of the classes above (e.g. “visible” property from GtkWidget)

12. GTK signals This is the basis for interactivity and response
Main loop and input interaction
Interaction generates a signal, which can be caught and used to trigger a function
Example: a button click, a checkbox filled or cleared

13. Important Python points
import gtk lets you use GTK library bindings
Create a GtkBuilder object
Use gtk.Builder.add_from_file( ) to load objects def __init__(self): self.builder = gtk.Builder() self.builder.add_from_file('prog.builder') # Now you can refer to elements using # the self.builder object

14. Element references
The gtk.Builder.get_object( ) function returns an object based on its name self.close_button = \ self.builder.get_object('close')

15. Simple example
easy-entry.py – Takes text entry from a dialog and outputs the text on the command line
Demonstrates very simple interface and signals
Window, buttons, text entry
Window deletion, “clicked” signal
GTK main loop

16. Two approaches
Write code, add GUI
Design GUI, write code to fit

17. Code first? For GUI wrappers around an existing program
Not all options are worth GUI-izing!
GConf keys (soon GSettings) can store some tweakable configuration

18. Design first? Know your user and use cases Who is this tool for?
How will they use it?
How will it integrate with other apps?
Draw a mockup first (paper is fine)

19. Using Glade for mockups
Use boxes liberally
GNOME Human Interface Guidelines provide layout help for a matching interface (Section 8, “Visual Design”)
Many standard dialogs are easy to create

20. Intermediate topics

21. Distributing your work
Write a setup.py file
The setup( ) function takes parameters such as simple sequences that let distutils do the work
MANIFEST.in file to include source content
Simple commands for builds, tarballs python setup.py --help-commands

22. Reminder: Program flow
XML file defines the GUI elements
Python code loads file into gtk.Builder object
Python code continues to refine GUI and assign interactivity through additional functions

23. PyGTK can change the UI
Not everything has to be written in the Glade file!
Assign label text and other content
Hide or show elements
Example: PulseCaster

24. I18n and L10n
I18n (internationalization) is the process of making code multilingual
L10n (localization) is the process of translating content
Don't restrict your audience to just English speakers

25. Adding i18n Transfer labels to your Python code
Add gettext function import gettext _ = lambda x: gettext.ldgettext('myprog', x)
Mark all strings with the _( ) function
But now what? How to get them into translatable formats?

26. Babel to the rescue! Install the python-babel package
Wraps around Python distutils to provide message (text string) extraction, for instance based on the _( ) function: python setup.py extract_messages

27. Thank you! Questions? pfrields@fedoraproject.org