Layout management in PyQt4

An important aspect in GUI programming is the layout management. Layout management is the way how we place the widgets on the window. The management can be done in two basic ways. We can use absolute positioning or layout classes.

Absolute positioning

The programmer specifies the position and the size of each widget in pixels. When you use absolute positioning, we have to understand the following limitations:

The following example will position widgets in absolute coordinates.

#!/usr/bin/python
# -*- coding: utf-8 -*-

"""
ZetCode PyQt4 tutorial 

This example shows three labels on a window
using absolute positioning. 

author: Jan Bodnar
website: zetcode.com 
last edited: October 2011
"""

import sys
from PyQt4 import QtGui

class Example(QtGui.QWidget):
    
    def __init__(self):
        super(Example, self).__init__()
        
        self.initUI()
        
    def initUI(self):
        
        lbl1 = QtGui.QLabel('ZetCode', self)
        lbl1.move(15, 10)

        lbl2 = QtGui.QLabel('tutorials', self)
        lbl2.move(35, 40)
        
        lbl3 = QtGui.QLabel('for programmers', self)
        lbl3.move(55, 70)        
        
        self.setGeometry(300, 300, 250, 150)
        self.setWindowTitle('Absolute')    
        self.show()
        
def main():
    
    app = QtGui.QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

We use the move() method to position our widgets. In our case these are labels. We position them by providing the x and y coordinates. The beginning of the coordinate system is at the left top corner. The x values grow from left to right. The y values grow from top to bottom.

lbl1 = QtGui.QLabel('Zetcode', self)
lbl1.move(15, 10)

The label widget is positioned at x=15 and y=10.

Absolute positioning
Figure: Absolute positioning

Box layout

Layout management with layout classes is much more flexible and practical. It is the preferred way to place widgets on a window. The QtGui.QHBoxLayout and QtGui.QVBoxLayout are basic layout classes that line up widgets horizontally and vertically.

Imagine that we wanted to place two buttons in the right bottom corner. To create such a layout, we will use one horizontal, and one vertical box. To create the necessary space, we will add a stretch factor.

#!/usr/bin/python
# -*- coding: utf-8 -*-

"""
ZetCode PyQt4 tutorial 

In this example, we position two push
buttons in the bottom-right corner 
of the window. 

author: Jan Bodnar
website: zetcode.com 
last edited: October 2011
"""

import sys
from PyQt4 import QtGui

class Example(QtGui.QWidget):
    
    def __init__(self):
        super(Example, self).__init__()
        
        self.initUI()
        
    def initUI(self):
        
        okButton = QtGui.QPushButton("OK")
        cancelButton = QtGui.QPushButton("Cancel")

        hbox = QtGui.QHBoxLayout()
        hbox.addStretch(1)
        hbox.addWidget(okButton)
        hbox.addWidget(cancelButton)

        vbox = QtGui.QVBoxLayout()
        vbox.addStretch(1)
        vbox.addLayout(hbox)
        
        self.setLayout(vbox)    
        
        self.setGeometry(300, 300, 300, 150)
        self.setWindowTitle('Buttons')    
        self.show()
        
def main():
    
    app = QtGui.QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

The example places two buttons in the bottom-right corner of the window. They stay there when we resize the application window. We use both a QtGui.HBoxLayout and a QtGui.QVBoxLayout.

okButton = QtGui.QPushButton("OK")
cancelButton = QtGui.QPushButton("Cancel")

Here we create two push buttons.

hbox = QtGui.QHBoxLayout()
hbox.addStretch(1)
hbox.addWidget(okButton)
hbox.addWidget(cancelButton)

We create a horizontal box layout and add a stretch factor and both buttons. The stretch adds a stretchable space before the two buttons. This will push them to the right of the window.

vbox = QtGui.QVBoxLayout()
vbox.addStretch(1)
vbox.addLayout(hbox)

To create the necessary layout, we put a horizontal layout into a vertical one. The stretch factor in the vertical box will push the horizontal box with the buttons to the bottom of the window.

self.setLayout(vbox)

Finally, we set the main layout of the window.

Buttons
Figure: Buttons

QtGui.QGridLayout

The most universal layout class is the grid layout. This layout divides the space into rows and columns. To create a grid layout, we use the QtGui.QGridLayout class.

#!/usr/bin/python
# -*- coding: utf-8 -*-

import sys
from PyQt4 import QtGui

"""
ZetCode PyQt4 tutorial 

In this example, we create a skeleton
of a calculator using a QtGui.QGridLayout.

author: Jan Bodnar
website: zetcode.com 
last edited: July 2014
"""

class Example(QtGui.QWidget):
    
    def __init__(self):
        super(Example, self).__init__()
        
        self.initUI()
        
    def initUI(self):
        
        grid = QtGui.QGridLayout()
        self.setLayout(grid)
 
        names = ['Cls', 'Bck', '', 'Close',
                 '7', '8', '9', '/',
                '4', '5', '6', '*',
                 '1', '2', '3', '-',
                '0', '.', '=', '+']
        
        positions = [(i,j) for i in range(5) for j in range(4)]
        
        for position, name in zip(positions, names):
            
            if name == '':
                continue
            button = QtGui.QPushButton(name)
            grid.addWidget(button, *position)
            
        self.move(300, 150)
        self.setWindowTitle('Calculator')
        self.show()
        
def main():
    app = QtGui.QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()

In our example, we create a grid of buttons.

grid = QtGui.QGridLayout()
self.setLayout(grid)

The instance of a QtGui.QGridLayout is created and set to be the layout for the application window.

names = ['Cls', 'Bck', '', 'Close',
            '7', '8', '9', '/',
        '4', '5', '6', '*',
            '1', '2', '3', '-',
        '0', '.', '=', '+']

These are the labels used later for buttons.

positions = [(i,j) for i in range(5) for j in range(4)]

We create a list of positions in the grid.

for position, name in zip(positions, names):
    
    if name == '':
        continue
    button = QtGui.QPushButton(name)
    grid.addWidget(button, *position)

Buttons are created and added to the layout with the addWidget() method.

Calculator skeleton
Figure: Calculator skeleton

Review example

Widgets can span multiple columns or rows in a grid. In the next example we illustrate this.

#!/usr/bin/python
# -*- coding: utf-8 -*-

"""
ZetCode PyQt4 tutorial 

In this example, we create a bit
more complicated window layout using
the QtGui.QGridLayout manager. 

author: Jan Bodnar
website: zetcode.com 
last edited: October 2011
"""

import sys
from PyQt4 import QtGui


class Example(QtGui.QWidget):
    
    def __init__(self):
        super(Example, self).__init__()
        
        self.initUI()
        
    def initUI(self):
        
        title = QtGui.QLabel('Title')
        author = QtGui.QLabel('Author')
        review = QtGui.QLabel('Review')

        titleEdit = QtGui.QLineEdit()
        authorEdit = QtGui.QLineEdit()
        reviewEdit = QtGui.QTextEdit()

        grid = QtGui.QGridLayout()
        grid.setSpacing(10)

        grid.addWidget(title, 1, 0)
        grid.addWidget(titleEdit, 1, 1)

        grid.addWidget(author, 2, 0)
        grid.addWidget(authorEdit, 2, 1)

        grid.addWidget(review, 3, 0)
        grid.addWidget(reviewEdit, 3, 1, 5, 1)
        
        self.setLayout(grid) 
        
        self.setGeometry(300, 300, 350, 300)
        self.setWindowTitle('Review')    
        self.show()
        
def main():
    
    app = QtGui.QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

We create a window in which we have three labels, two line edits, and one text edit widget. The layout is done with the QtGui.QGridLayout.

grid = QtGui.QGridLayout()
grid.setSpacing(10)

We create a grid layout and set spacing between widgets.

grid.addWidget(reviewEdit, 3, 1, 5, 1)

If we add a widget to a grid, we can provide row span and column span of the widget. In our case, we make the reviewEdit widget span 5 rows.

Review example
Figure: Review example

This part of the PyQt4 tutorial was dedicated to layout management.