#PYQT5 Gui

PyQt - Signals & Slots - Unlike a console mode application, which is executed in a sequential manner, a GUI based application is event driven. Functions or methods are executed in respo.

I have never had the requirement to develop a Gui in Python, and after having a look at some of the available frameworks - I have come back to Qt. This was rather a surprise to me also !! But none of the other frameworks I tried had the signal/slot (callbacks if you like) that Qt provided.

#Getting going in PyQt

The most difficult issue is to try and get Qt compiled and installed - I did this initially on a Mac (using PyVenv) and it was very painless - the general steps are as follows.

virtualenv -p /usr/local/bin/python3.4 pyqt

• install xcode
• install the Command Line Tools (open Xcode > Preferences > Downloads)
• install Qt libraries (qt-opensource-mac-x64-clang-5.2.1.dmg)
• install python 3.4
• create a virtual env (i.e. ~/.env/ariane_mail)
• unzip and compile SIP and PyQt

#Commands

vi /Users/tim/Qt5.2.1/5.2.1/clang_64/mkspecs/qdevice.priAnd make file look like

And now Build QT

#Test it all worked

#PyQt Running - now what !!

Well the first thing to get going is the designer interface - I cheated and cleated an Alias something along the lines of..

Do a simple gui and save the output.

##Convert ui to Python code

This is super easy - and the following commands should do this for you

Note -x will add a basic QtApplication so you can just run the code.

When you are happy with this - then you should be able to look at the example I have provided.

#My Example

Before I went any further with some development tasks, I wanted to make sure that I could do the following

• Link a Button (or QT Object) to some custom method
• Create a detached process - that could do something
• Create a custom signal - and attach it to a custom slot
• Create QThread based class (This can emit Signals for the QApp)
• Linked Thread's Signal to Widgets Slot

In this part of the PyQt5 tutorial we learn some basic functionality. The examples show a tooltip and an icon, close a window, show a message box and centera window on the desktop.

Simple example

This is a simple example showing a small window. Yet we can do a lotwith this window. We can resize it, maximise it or minimise it. This requires a lot of coding. Someone already coded this functionality. Because it is repeated in most applications, there is no need to code it over again. PyQt5 is a high level toolkit. If we would code in a lower level toolkit, the following code example could easily have hundreds of lines.

The above code example shows a small window on the screen.

Here we provide the necessary imports. The basic widgets are located in PyQt5.QtWidgets module.

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Every PyQt5 application must create an application object. The sys.argv parameter is a list of arguments from a command line. Python scripts can be run from the shell. It is a way how we can control the startup of our scripts.

The QWidget widget is the base class of all user interface objects in PyQt5. We provide the default constructor for QWidget. The default constructor has no parent. A widget with no parent is called a window.

The resize() method resizes the widget. It is 250px wide and 150px high.

The move() method moves the widget to a positionon the screen at x=300, y=300 coordinates.

We set the title of the window with setWindowTitle(). The title is shown in the titlebar.

The show() method displays the widget on the screen. A widget is first created in memory and later shown on the screen.

Finally, we enter the mainloop of the application. The event handling starts from this point. The mainloop receives events from the window system and dispatches them to the application widgets.The mainloop ends if we call the exit() method or the main widget is destroyed. The sys.exit() method ensures a clean exit. The environment will be informed how the application ended.

The exec_() method has an underscore. It is because the exec is a Python keyword. And thus, exec_() was used instead.

Pyqt5 Signals And Slots Example List

An application icon

The application icon is a small image which is usually displayedin the top left corner of the titlebar. In the following example we will show how we do it in PyQt5. We will also introduce some new methods.

Some environments do not display icons in the titlebars. We need to enable them.See my answeron Stackoverflow for a solution, if you are seeing no icons.

The previous example was coded in a procedural style. Python programming language supports both procedural and object oriented programming styles. Programming in PyQt5 means programming in OOP.

Three important things in object oriented programming are classes, data, and methods. Here we create a new class called Example. The Example class inherits from the QWidget class. This means that we call two constructors: the first one for the Example class and the second one for the inherited class. The super()method returns the parent object of the Example class and we call its constructor. The __init__() method is a constructor method in Python language.

The creation of the GUI is delegated to the initUI() method.

All three methods have been inherited from the QWidget class. The setGeometry() does two things: it locates the window on the screen and sets it size. The first two parameters are the x and y positions of the window. The third is the width and the fourth is the height of the window. In fact, it combines the resize() and move() methods in one method. The last method sets the application icon. To do this, we have created a QIcon object. The QIcon receives the path to our icon to be displayed.

The application and example objects are created. The main loop is started.

Showing a tooltip

We can provide a balloon help for any of our widgets.

In this example, we show a tooltip for two PyQt5 widgets.

This static method sets a font used to render tooltips.We use a 10pt SansSerif font.

To create a tooltip, we call the setTooltip() method. We can use rich text formatting.

We create a push button widget and set a tooltip for it.

The button is being resized and moved on the window. The sizeHint()method gives a recommended size for the button.

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Closing a window

The obvious way to close a window is to click on the x mark on the titlebar. In the next example, we show how we can programatically close our window.We will briefly touch signals and slots.

The following is the constructor of a QPushButton widget that we use in our example.

The text parameter is a text that will be displayed on the button. The parent is a widget on which we place our button. In our case it will be a QWidget. Widgets of an application form a hierarchy.In this hierarchy, most widgets have their parents. Widgets without parents are toplevel windows.

In this example, we create a quit button. Upon clicking on the button, the application terminates.

We create a push button. The button is an instance of the QPushButton class. The first parameter of the constructor is the label of the button. The second parameter is the parent widget. The parent widget is the Example widget, which is a QWidget by inheritance.

The event processing system in PyQt5 is built with the signal & slot mechanism. If we click on the button, the signal clicked is emitted. The slot can be a Qt slot or any Python callable.

QCoreApplication, which is retrieved with QApplication.instance(), contains the main event loop—it processes and dispatches all events. The clicked signal is connected to the quit() method which terminates the application. The communication is done between two objects: the sender and the receiver. The sender is the push button, the receiver is the application object.

Message Box

By default, if we click on the x button on the titlebar, the QWidget is closed. Sometimes we want to modify this default behaviour. For example, if we have a file opened in an editorto which we did some changes. Casino militar campo marte bodas. We show a message box to confirm the action.

If we close a QWidget, the QCloseEvent is generated. To modify the widget behaviour we need to reimplement the closeEvent() event handler.

We show a message box with two buttons: Yes and No. The first string appears on the titlebar. The second string is the message text displayed by the dialog. The third argument specifies the combination of buttons appearing in the dialog. The last parameter is the default button. It is the button which has initially the keyboard focus. The return value is stored in the reply variable.

Here we test the return value. If we click the Yes button, we accept the event which leads to the closure of the widget and to the termination of the application. Otherwise we ignore the close event.

Centering window on the screen

The following script shows how we can center a window on the desktop screen.

The QDesktopWidget class provides information about the user's desktop, including the screen size.

Pyqt Signals And Slots Example

The code that will center the window is placed in the custom center() method.

Pyqt5 Emit Signal

We get a rectangle specifying the geometry of the main window. This includes any window frame.

We figure out the screen resolution of our monitor. And from this resolution, we get the center point.

Tutorial Pyqt5 Signals And Slots

Our rectangle has already its width and height. Now we set the center of the rectangle to the center of the screen. The rectangle's size is unchanged.

We move the top-left point of the application window to the top-left point of the qr rectangle, thus centering the window on our screen.

Pyqt5 Signals And Slots Example 3

In this part of the PyQt5 tutorial, we have created simple code examplesin PyQt5.