Question

Widgets are basic building blocks of an application. PyQt5 has a wide range of various widgets, including buttons, check boxes, sliders, or list boxes. In this section of the tutorial, we will describe several useful widgets: a QCheckBox , a ToggleButton , a QSlider , a QProgressBar , and a QCalendarWidget .

QCheckBox

A QCheckBox is a widget that has two states: on and off. It is a box with a label. Checkboxes are typically used to represent features in an application that can be enabled or disabled.

#!/usr/bin/python3
# -*- coding: utf-8 -*-

"""
ZetCode PyQt5 tutorial 

In this example, a QCheckBox widget
is used to toggle the title of a window.

author: Jan Bodnar
website: zetcode.com 
last edited: January 2015
"""

import sys
from PyQt5.QtWidgets import QWidget, QCheckBox, QApplication
from PyQt5.QtCore import Qt


class Example(QWidget):
  
  def __init__(self):
    super().__init__()
    
    self.initUI()
    
    
  def initUI(self):    

    cb = QCheckBox('Show title', self)
    cb.move(20, 20)
    cb.toggle()
    cb.stateChanged.connect(self.changeTitle)
    
    self.setGeometry(300, 300, 250, 150)
    self.setWindowTitle('QCheckBox')
    self.show()
    
    
  def changeTitle(self, state):
    
    if state == Qt.Checked:
      self.setWindowTitle('QCheckBox')
    else:
      self.setWindowTitle('')
      
    
if __name__ == '__main__':
  
  app = QApplication(sys.argv)
  ex = Example()
  sys.exit(app.exec_())

In our example, we will create a checkbox that will toggle the window title.

cb = QCheckBox('Show title', self)

This is a QCheckBox constructor.

cb.toggle()

We have set the window title, so we must also check the checkbox. By default, the window title is not set and the checkbox is unchecked.

cb.stateChanged.connect(self.changeTitle)

We connect the user defined changeTitle() method to the stateChanged signal. The changeTitle() method will toggle the window title.

def changeTitle(self, state):
  
  if state == Qt.Checked:
    self.setWindowTitle('QCheckBox')
  else:
    self.setWindowTitle('')

The state of the widget is given to the changeTitle() method in the state variable. If the widget is checked, we set a title of the window. Otherwise, we set an empty string to the titlebar.

Figure: QCheckBox

Toggle button

A toggle button is a QPushButton in a special mode. It is a button that has two states: pressed and not pressed. We toggle between these two states by clicking on it. There are situations where this functionality fits well.

#!/usr/bin/python3
# -*- coding: utf-8 -*-

"""
ZetCode PyQt5 tutorial 

In this example, we create three toggle buttons.
They will control the background colour of a 
QFrame. 

author: Jan Bodnar
website: zetcode.com 
last edited: January 2015
"""

import sys
from PyQt5.QtWidgets import (QWidget, QPushButton, 
  QFrame, QApplication)
from PyQt5.QtGui import QColor


class Example(QWidget):
  
  def __init__(self):
    super().__init__()
    
    self.initUI()
    
    
  def initUI(self):    

    self.col = QColor(0, 0, 0)     

    redb = QPushButton('Red', self)
    redb.setCheckable(True)
    redb.move(10, 10)

    redb.clicked[bool].connect(self.setColor)

    redb = QPushButton('Green', self)
    redb.setCheckable(True)
    redb.move(10, 60)

    redb.clicked[bool].connect(self.setColor)

    blueb = QPushButton('Blue', self)
    blueb.setCheckable(True)
    blueb.move(10, 110)

    blueb.clicked[bool].connect(self.setColor)

    self.square = QFrame(self)
    self.square.setGeometry(150, 20, 100, 100)
    self.square.setStyleSheet("QWidget { background-color: %s }" %  
      self.col.name())
    
    self.setGeometry(300, 300, 280, 170)
    self.setWindowTitle('Toggle button')
    self.show()
    
    
  def setColor(self, pressed):
    
    source = self.sender()
    
    if pressed:
      val = 255
    else: val = 0
            
    if source.text() == "Red":
      self.col.setRed(val)        
    elif source.text() == "Green":
      self.col.setGreen(val)       
    else:
      self.col.setBlue(val) 
      
    self.square.setStyleSheet("QFrame { background-color: %s }" %
      self.col.name())  
     
     
if __name__ == '__main__':
  
  app = QApplication(sys.argv)
  ex = Example()
  sys.exit(app.exec_())

In our example, we create three toggle buttons and a QWidget . We set the background colour of the QWidget to black. The toggle buttons will toggle the red, green, and blue parts of the colour value. The background colour will depend on which toggle buttons we have pressed.

self.col = QColor(0, 0, 0)  

This is the initial, black colour value.

redb = QPushButton('Red', self)
redb.setCheckable(True)
redb.move(10, 10)

To create a toggle button, we create a QPushButton and make it checkable by calling the setCheckable() method.

redb.clicked[bool].connect(self.setColor)

We connect a clicked signal to our user defined method. We use the clicked signal that operates with a Boolean value.

source = self.sender()

We get the button which was toggled.

if source.text() == "Red":
  self.col.setRed(val)   

In case it is a red button, we update the red part of the colour accordingly.

self.square.setStyleSheet("QFrame { background-color: %s }" %
  self.col.name())   

We use style sheets to change the background colour.

Figure: Toggle button

QSlider

A QSlider is a widget that has a simple handle. This handle can be pulled back and forth. This way we are choosing a value for a specific task. Sometimes using a slider is more natural than entering a number or using a spin box.

In our example we will show one slider and one label. The label will display an image. The slider will control the label.

#!/usr/bin/python3
# -*- coding: utf-8 -*-

"""
ZetCode PyQt5 tutorial 

This example shows a QSlider widget.

author: Jan Bodnar
website: zetcode.com 
last edited: January 2015
"""

import sys
from PyQt5.QtWidgets import (QWidget, QSlider, 
  QLabel, QApplication)
from PyQt5.QtCore import Qt
from PyQt5.QtGui import QPixmap


class Example(QWidget):
  
  def __init__(self):
    super().__init__()
    
    self.initUI()
    
    
  def initUI(self):    

    sld = QSlider(Qt.Horizontal, self)
    sld.setFocusPolicy(Qt.NoFocus)
    sld.setGeometry(30, 40, 100, 30)
    sld.valueChanged[int].connect(self.changeValue)
    
    self.label = QLabel(self)
    self.label.setPixmap(QPixmap('mute.png'))
    self.label.setGeometry(160, 40, 80, 30)
    
    self.setGeometry(300, 300, 280, 170)
    self.setWindowTitle('QSlider')
    self.show()
    
    
  def changeValue(self, value):

    if value == 0:
      self.label.setPixmap(QPixmap('mute.png'))
    elif value > 0 and value <= 30:
      self.label.setPixmap(QPixmap('min.png'))
    elif value > 30 and value < 80:
      self.label.setPixmap(QPixmap('med.png'))
    else:
      self.label.setPixmap(QPixmap('max.png'))
      

if __name__ == '__main__':

  app = QApplication(sys.argv)
  ex = Example()
  sys.exit(app.exec_())    

In our example we simulate a volume control. By dragging the handle of a slider, we change an image on the label.

sld = QSlider(Qt.Horizontal, self)

Here we create a horizontal QSlider .

self.label = QLabel(self)
self.label.setPixmap(QPixmap('mute.png'))

We create a QLabel widget and set an initial mute image to it.

sld.valueChanged[int].connect(self.changeValue)

We connect the valueChanged signal to the user defined changeValue() method.

if value == 0:
  self.label.setPixmap(QPixmap('mute.png'))
...

Based on the value of the slider, we set an image to the label. In the above code, we set the mute.png image to the label if the slider is equal to zero.

Figure: QSlider widget

QProgressBar

A progress bar is a widget that is used when we process lengthy tasks. It is animated so that the user knows that the task is progressing. The QProgressBar widget provides a horizontal or a vertical progress bar in PyQt5 toolkit. The programmer can set the minimum and maximum value for the progress bar. The default values are 0 and 99.

#!/usr/bin/python3
# -*- coding: utf-8 -*-

"""
ZetCode PyQt5 tutorial 

This example shows a QProgressBar widget.

author: Jan Bodnar
website: zetcode.com 
last edited: January 2015
"""

import sys
from PyQt5.QtWidgets import (QWidget, QProgressBar, 
  QPushButton, QApplication)
from PyQt5.QtCore import QBasicTimer


class Example(QWidget):
  
  def __init__(self):
    super().__init__()
    
    self.initUI()
    
    
  def initUI(self):    

    self.pbar = QProgressBar(self)
    self.pbar.setGeometry(30, 40, 200, 25)

    self.btn = QPushButton('Start', self)
    self.btn.move(40, 80)
    self.btn.clicked.connect(self.doAction)

    self.timer = QBasicTimer()
    self.step = 0
    
    self.setGeometry(300, 300, 280, 170)
    self.setWindowTitle('QProgressBar')
    self.show()
    
    
  def timerEvent(self, e):
    
    if self.step >= 100:
      self.timer.stop()
      self.btn.setText('Finished')
      return
      
    self.step = self.step + 1
    self.pbar.setValue(self.step)
    

  def doAction(self):
    
    if self.timer.isActive():
      self.timer.stop()
      self.btn.setText('Start')
    else:
      self.timer.start(100, self)
      self.btn.setText('Stop')
      
    
if __name__ == '__main__':
  
  app = QApplication(sys.argv)
  ex = Example()
  sys.exit(app.exec_())

In our example we have a horizontal progress bar and a push button. The push button starts and stops the progress bar.

self.pbar = QProgressBar(self)

This is a QProgressBar constructor.

self.timer = QtCore.QBasicTimer()

To activate the progress bar, we use a timer object.

self.timer.start(100, self)

To launch a timer event, we call its start() method. This method has two parameters: the timeout and the object which will receive the events.

def timerEvent(self, e):
  
  if self.step >= 100:
  
    self.timer.stop()
    self.btn.setText('Finished')
    return
    
  self.step = self.step + 1
  self.pbar.setValue(self.step)

Each QObject and its descendants have a timerEvent() event handler. In order to react to timer events, we reimplement the event handler.

def doAction(self):
  
  if self.timer.isActive():
    self.timer.stop()
    self.btn.setText('Start')
    
  else:
    self.timer.start(100, self)
    self.btn.setText('Stop')

Inside the doAction() method, we start and stop the timer.

Figure: QProgressBar

QCalendarWidget

A QCalendarWidget provides a monthly based calendar widget. It allows a user to select a date in a simple and intuitive way.

#!/usr/bin/python3
# -*- coding: utf-8 -*-

"""
ZetCode PyQt5 tutorial 

This example shows a QCalendarWidget widget.

author: Jan Bodnar
website: zetcode.com 
last edited: January 2015
"""

import sys
from PyQt5.QtWidgets import (QWidget, QCalendarWidget, 
  QLabel, QApplication)
from PyQt5.QtCore import QDate


class Example(QWidget):
  
  def __init__(self):
    super().__init__()
    
    self.initUI()
    
    
  def initUI(self):    

    cal = QCalendarWidget(self)
    cal.setGridVisible(True)
    cal.move(20, 20)
    cal.clicked[QDate].connect(self.showDate)
    
    self.lbl = QLabel(self)
    date = cal.selectedDate()
    self.lbl.setText(date.toString())
    self.lbl.move(130, 260)
    
    self.setGeometry(300, 300, 350, 300)
    self.setWindowTitle('Calendar')
    self.show()
    
    
  def showDate(self, date):   
    
    self.lbl.setText(date.toString())
    
    
if __name__ == '__main__':
  
  app = QApplication(sys.argv)
  ex = Example()
  sys.exit(app.exec_())

The example has a calendar widget and a label widget. The currently selected date is displayed in the label widget.

cal = QCalendarWidget(self)

The QCalendarWidget is created.

cal.clicked[QDate].connect(self.showDate)

If we select a date from the widget, a clicked[QDate] signal is emitted. We connect this signal to the user defined showDate() method.

def showDate(self, date):   
  
  self.lbl.setText(date.toString())

We retrieve the selected date by calling the selectedDate() method. Then we transform the date object into string and set it to the label widget.

In this part of the PyQt5 tutorial, we covered several widgets.