Chapter 6. Embedding Matplotlib in Qt 5

There are several GUI libraries available, and one widely used library is Qt. In this book, we will be using Qt 5, the latest major version of this library. Unless explicitly mentioned, we are referring to Qt 5 when we simply state Qt throughout the chapter.

We will follow a similar progression to that in Chapter 5, Embedding Matplotlib in GTK+3, and we will present similar examples but this time written in Qt.

We believe that this method will allow us to directly compare the libraries, and it has the advantage of not leaving the How would I write something with library X? question unanswered.

In this chapter, we will learn how to:

• Embed a Matplotlib figure into a Qt widget
• Embed a figure and navigation toolbar into a Qt widget
• Use events to update a Matplotlib plot in real time
• Use QT Designer to draw a GUI and then use it with Matplotlib in a simple Python application

We will begin by giving an introduction to the library.

A brief introduction to Qt 5 and PyQt 5

Qt is a cross-platform application development framework widely used for graphical programs (GUI) and also for non-GUI tools.

Qt was developed by Trolltech (now owned by Nokia), and it's probably best known for being the foundation of the K Desktop Environment (KDE) for Linux.

The Qt toolkit is a collection of classes made to simplify the creation of programs. Qt is more than just a GUI toolkit. It includes components for abstractions of network sockets, threads, Unicode, regular expressions, SQL databases, SVG, OpenGL, and XML. It also has a fully functional web browser, help system, multimedia framework, and rich collection of GUI widgets.

Qt is available on several platforms, particularly Unix/Linux, Windows, macOS X, and also some embedded devices. As it uses native APIs of the platform to render the Qt controls, applications developed with Qt have a look and feel that fits the running environment (without looking like something alien in it).

Though...

Differences between Qt 4 and PyQt 4

PyQt is a comprehensive set of Python bindings for the Qt framework. However, PyQt 5 is not backward compatible with PyQt 4. It is noteworthy that PyQt 5 does not support any part of the Qt API that are marked as deprecated or obsolete in Qt v5.0. However, it is possible that some of these are included accidentally. If included, they are considered bugs and will be removed when found.

If you are familiar with Qt 4 or have read the first edition of this book, one thing to note is that the signals and slots of are no longer supported. Therefore, the following are not implemented in PyQt 5:

• QtScript
• QObject.connect()
• QObject.emit()
• SIGNAL()
• SLOT()

Also, there is a modification in disconnect() as it no longer takes arguments and will disconnect all connections to the QObject instance when invoked.

However, new modules have been introduced, such as the following:

• QtBluetooth
• QtPositioning
• Enginio

Let's start with a very simple example—calling a window. Again for best performance...

Summary

GUI design by using QT Creator/ QT Designer has enough material for a book on its own. Therefore, in this chapter, we aimed to show you just a glimpse of GUI design through PyQt 5. Upon finishing this chapter, the readers should now understand how to embed a figure in a QWidget, use the layout manager to pack a figure in a QWidget, create a timer, react to events and update a Matplotlib graph accordingly, and use QT Designer to draw a simple GUI for Matplotlib embedding.

We are now ready to learn another GUI library, wxWidgets.