Python | Introduction to PyQt5

There are so many options provided by Python to develop GUI application and PyQt5 is one of them. PyQt5 is cross-platform GUI toolkit, a set of python bindings for Qt v5. One can develop an interactive desktop application with so much ease because of the tools and simplicity provided by this library. A GUI application consists of Front-end and Back-end. PyQt5 has provided a tool called 'QtDesigner' to design the front-end by drag and drop method so that development can become faster and one can give more time on back-end stuff. Installation: First, we need to install PyQt5 library. For this, type the following command in the terminal or command prompt:

pip install pyqt5

If successfully installed one can verify it by running the code:

>>>import PyQt5

PyQt5 provides lots of tools and QtDesigner is one of them. For this run this command:

pip install PyQt5-tools

Create your first app -

This is a simple app having a single button in the window. After clicking that button a message will appear "You clicked me". Let's start.

• First of all, we need to find QtDesigner to create the front-end part. - QtDesigner is present at 'site-packages/pyqt5_tools' - For finding the location of site-packages write the following python code using any editor of your choice and then run:

>>> import site >>> site.getsitepackages()

• - Run the application named 'designer'.
• A window will open as shown in the figure: select the 'Dialog without Button' option and click 'Create'
• At the left side of the designer there will be various widgets which can be dragged and dropped in our window according to our requirement.
• Find and drag-and-drop 'Push Button' and 'Label'.
• Change the text inside the widgets by right clicking it and selecting 'Change plain text'. Keep the text of the Label blank.
• We have created our front-end layout, just save it at your desired location.Remember, this file will have .ui as extension.
• We need to convert the .ui file into .py file to get the python form of the widgets and attach necessary event listeners to them.

Converting .ui file into .py file:

• For this we have to go to sitepackages directory in terminal or command prompt and run the command as shown below. Getting the location of sitepackages is mentioned previously.

>>> cd "C:\\Users\\......\\Programs\\Python\\Python36-32\\lib\\site-packages" [Location of sitepackages] >>> pyuic5 "C:\Users\......\FILENAME.ui"[Exact location of .ui file] -o " C:\Users\.......\FILENAME.py" [Location where want to put .py file]

• Finally we will add signals and slot in the python code to make it fully functional.

widget.signal.connect(slot)

• A signal is emitted by widgets after the occurrence of a certain kind of event like a click, Double click, etc. A slot is any callable function which will perform some action after the occurrence of an event.
• Run the app and click the button.

Below is the code - 

import sys from PyQt5 import QtCore, QtGui, QtWidgets class Ui_Dialog(object): def setupUi(self, Dialog): Dialog.setObjectName("Dialog") Dialog.resize(400, 300) self.pushButton = QtWidgets.QPushButton(Dialog) self.pushButton.setGeometry(QtCore.QRect(150, 70, 93, 28)) self.label = QtWidgets.QLabel(Dialog) self.label.setGeometry(QtCore.QRect(130, 149, 151, 31)) self.label.setText("") self.retranslateUi(Dialog) QtCore.QMetaObject.connectSlotsByName(Dialog) # adding signal and slot self.pushButton.clicked.connect(self.showmsg) def retranslateUi(self, Dialog): _translate = QtCore.QCoreApplication.translate Dialog.setWindowTitle(_translate("Dialog", "Dialog")) self.pushButton.setText(_translate("Dialog", "Click")) def showmsg(self): # slot self.label.setText("You clicked me") if __name__ == "__main__": app = QtWidgets.QApplication(sys.argv) MainWindow = QtWidgets.QMainWindow() ui = Ui_Dialog() ui.setupUi(MainWindow) MainWindow.show() sys.exit(app.exec_())