PyQt by Example. The backend The most recent version of this session (in RST format) is always available at GitHub’s master tree as tut1.txt Since we are developing a TODO application, we need a backend that handles the storage, retrieval and general managing of TODO tasks. To do that the simplest possible way, I will do it using Elixir, “A declarative layer over the SQLAlchemy Object-Relational Mapper”. If that sounded very scary, don’t worry. What that means is “a way to create objects that are automatically stored in a database”.
Here is the code, with comments, for our backend, called todo.py. The Main Window Now, let’s start with the fun part: PyQt! I recommend using designer to create your graphical interfaces. And here is the Qt Designer file for it: window.ui. This is how it looks in designer: The main window, in designer. What you see is a “Main Window”. You can see how this window looks by using “Form” -> “Preview” in designer. QGraphicsScene. Introduction This is not really part of my PyQt by Example series but since it’s a totally unrelated topic that would be impossible to connect to it, but is still a PyQt tutorial and follows the same concept… whatever, here it is.
In this tutorial I will explain QGraphicsScene (QGS for short) and its related classes. What are they for, you may ask? Well, the answer is: they are for cool stuff. You don’t need QGS for CRUD. You don’t need QGS for office applications. You don’t need QGS for boring stuff. How does it work You can think of a QGraphicsScene as a stage, filled with actors. An item can be of different kinds: A text A shape (like a circle or a polygon) A picture A widget (yes, any Qt widget works!) Then, you can have one or more “cameras” looking at the stage. Keep this in mind, because it’s very important: One QGraphicsScene can contain any number of QGraphicsItems.
So, having said that, let’s start doing code. PyQt. PyQt is a set of Python v2 and v3 bindings for Digia's Qt application framework and runs on all platforms supported by Qt including Windows, MacOS/X and Linux. PyQt5 supports Qt v5. PyQt4 supports Qt v4 and will build against Qt v5. The bindings are implemented as a set of Python modules and contain over 620 classes. Digia have announced that support for Qt v4 will cease at the end of 2015. PyQt5 and Qt v5 are strongly recommended for all new development. PyQt is dual licensed on all supported platforms under the GNU GPL v3 and the Riverbank Commercial License. PyQt does not include a copy of Qt. PyQt Components A description of the components of PyQt5 can be found in the PyQt5 Reference Guide. A description of the components of PyQt4 can be found in the PyQt4 Reference Guide.
Why PyQt? PyQt brings together the Qt C++ cross-platform application framework and the cross-platform interpreted language Python. Qt is more than a GUI toolkit. PyQt combines all the advantages of Qt and Python. Events and Signals in PyQt4. In this part of the PyQt4 programming tutorial, we will explore events and signals occurring in applications. Events All GUI applications are event-driven. Events are generated mainly by the user of an application. But they can be generated by other means as well: e.g. an Internet connection, a window manager, or a timer.
In the event model, there are three participants: event source event object event target The event source is the object whose state changes. PyQt4 has a unique signal and slot mechanism to deal with events. New API PyQt4.5 introduced a new style API for working with signals and slots. QtCore.QObject.connect(button, QtCore.SIGNAL('clicked()'), self.onClicked) This is the old style API. button.clicked.connect(self.onClicked) The new style adheres more to the Python standards.
Signals & Slots This is a simple example demonstrating signals and slots in PyQt4. #! In our example, we display a QtGui.QLCDNumber and a QtGui.QSlider. Sld.valueChanged.connect(lcd.display) #! Event sender #! #! 6: Qt Reference Documentation - Iceweasel.