# Python Programming/PyQt4

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WARNING: The examples on this page are a mixture of PyQt3 and PyQt4 - use with caution!
This tutorial aims to provide a hands-on guide to learn the basics of building a small Qt4 application in Python.
To follow this tutorial, you should have basic Python knowledge. However, knowledge of Qt4 is not necessary. I'm using Linux in these examples and am assuming you already have a working installation of Python and PyQt4. To test this, open a Python shell (by typing 'Python' in a console to start the interactive interpreter) and type:
If no error message appears, you should be ready to go.
The examples in this tutorial as easy as possible, showing useful ways to write and structure your program. It is important that you read the source code of the example files, most of the explanations are in the code. The best way to get comfortable with PyQt is play around with the examples and try to change things.

## Hello, world!

Let's start easy: popping up a window and displaying something. The following small program will pop up a window showing "Hello, world!".
About 7 lines of code, and that's about as easy as it can get.

## A Button

Let's add some interaction! We'll replace the label saying "Hello, World!" with a button and assign an action to it. This assignment is done by connecting a signal, an event which is sent out when the button is pushed, to a slot, which is an action, normally a function that is run in the case of that event.
You can imagine that coding this way is not scalable nor the way you'll want to continue working. So let's make that stuff pythonic, adding structure and actually using object-orientation in it. We create our own application class, derived from a QApplication and put the customization of the application into its methods: One method to build up the widgets and a slot which contains the code that's executed when a signal is received.

## GUI Coding

... so we want to use Qt3 Designer for creating our GUI. In the picture, you can see a simple GUI, with in green letters the names of the widgets. What we are going to do is We compile the .ui file from Qt designer into a python class We subclass that class and use it as our mainWidget This way, we're able to change the user interface afterwards from Qt designer, without having it messing around in the code we added.
makes a Python file from it which we can work with.
The way our program works can be described like this: We fill in the lineedit Clicking the add button will be connected to a method that reads the text from the lineedit, makes a listviewitem out of it and adds that to our listview. Clicking the deletebutton will delete the currently selected item from the listview. Here's the heavily commented code (only works in PyQt3):
also this code is useful and it works on PyQt4 and it has many useful options

## Useful to Know

Creating the GUI in Qt Designer not only makes creating the GUI easier, but it's also a great learning tool. You can test what a widget looks like, see what's available in Qt, and have a look at properties you might want to use.
The C++ API documentation is also a very useful (read: necessary) tool when working with PyQt. The API translation is straightforward, and after a little experience, you'll find the developers API docs one of the tools you really need. When working from KDE, konqueror's default shortcut is qt:[widgetname], so [alt]+[F2], "qt:qbutton directly takes you to the right API documentation page. Trolltech's doc section has much more documentation which you might want to have a look at.
The first 3 examples in this tutorial have been created using PyQt4, the last one uses syntax that only works with PyQt3.
Note: The previous version of this page (applicable to pyqt3) is/was available at http://vizzzion.org/?id=pyqt.
This document is published under the GNU Free Documentation License.
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