One of the most advanced packages for Gui development in Python is PyQt5. According to Christian Tismer, the maintainer of Pyside2, PyQt5 has some 25,000 functions for you to use. That’s a really big library. However, if you want to distribute your app commercially, you need to purchase a license from the Qt company. Fortunately enough, PySide2 allows you the same liberty as Free/Libre Software. Let’s see how we can migrate a typical PyQt5 app to PySide2.
Python3
import sysfrom PyQt5.QtWidgets import (QGridLayout)from PyQt5.QtWidgets import (QMainWindow)from PyQt5.QtWidgets import (QApplication)from PyQt5.QtWidgets import ( QWidget, QPushButton, QLabel, QLineEdit )from PyQt5.QtCore import Qtfrom PyQt5.QtGui import (QPixmap,QIcon)class Window(QMainWindow): def __init__(self, parent = None): super().__init__(parent) self.setWindowTitle('PyQt5 Demo App') self.initGui() def initGui(self): self.layout = QGridLayout() self.window = QWidget() self.window.setLayout(self.layout) self.setCentralWidget(self.window) self.num1_label = QLabel('Enter first number:') self.num1_label.setAlignment(Qt.AlignCenter) self.text_box1 = QLineEdit() self.num2_label = QLabel('Enter second number:') self.text_box2 = QLineEdit() self.get_answer = QPushButton() calculate_icon = QPixmap('path_to_image.png') self.get_answer.setIcon(QIcon(calculate_icon)) self.answer_label = QLabel('---') self.layout.addWidget(self.num1_label, 0, 0) self.layout.addWidget(self.text_box1, 1, 0) self.layout.addWidget(self.num2_label, 2, 0) self.layout.addWidget(self.text_box2, 3, 0) self.layout.addWidget(self.get_answer, 4, 0) self.layout.addWidget(self.answer_label, 5, 0)if __name__ == '__main__': app = QApplication(sys.argv) win = Window() win.show() sys.exit(app.exec_()) |
Output: 
We’ve deliberately made use of an example that uses QtWidget, QtCore and QtGui. One thing to do is to take on good practice. it about avoiding from X import *. Namespacing our imports has the advantage of learning what falls under what module.
Python3
import sysfrom PyQt5 import QtWidgetsfrom PyQt5 import QtCorefrom PyQt5 import QtGui |
Now, change our code to the following where we namespaced our imports. QMainWindow becomes QtWidgets.QMainWindow and so on –
Python3
class Window(QtWidgets.QMainWindow): def __init__(self, parent = None): super().__init__(parent) self.setWindowTitle('PyQt5 Demo App') self.initGui() def initGui(self): self.layout = QtWidgets.QGridLayout() self.window = QtWidgets.QWidget() self.window.setLayout(self.layout) self.setCentralWidget(self.window) self.num1_label = QtWidgets.QLabel('Enter first number:') self.num1_label.setAlignment(QtCore.Qt.AlignCenter) self.text_box1 = QtWidgets.QLineEdit() self.num2_label = QtWidgets.QLabel('Enter second number:') self.text_box2 = QtWidgets.QLineEdit() self.get_answer = QtWidgets.QPushButton() calculate_icon = QtGui.QPixmap('path_to_image.png') self.get_answer.setIcon(QtGui.QIcon(calculate_icon)) self.answer_label = QtWidgets.QLabel('---') self.layout.addWidget(self.num1_label, 0, 0) self.layout.addWidget(self.text_box1, 1, 0) self.layout.addWidget(self.num2_label, 2, 0) self.layout.addWidget(self.text_box2, 3, 0) self.layout.addWidget(self.get_answer, 4, 0) self.layout.addWidget(self.answer_label, 5, 0)if __name__ == '__main__': app = QtWidgets.QApplication(sys.argv) win = Window() win.show() sys.exit(app.exec_()) |
Converting To Pyside2 Converting our app to PySide2 is as simple as changing our imports to
Python3
import sysfrom PySide2 import QtWidgetsfrom PySide2 import QtCorefrom PySide2 import QtGui |
Caveats to look out for –
For most uses, migrating means adjusting imports, defining functions and using supported functions only.
- One thing to look out is app.exec_. exec_ was used as exec is a Python2 keyword. Under Python3, PyQt5 allows the use of exec but not PySide2. PyQt5 supports both sys.exit(app.exec_()) and sys.exit(app.exec()) but PySide2 supports only app.exec_().
- The second thing is signal and slots. Under PyQt5 it’s QtCore.pyqtSignal and QtCore.pyqtSlot and under PySide2 it’s QtCore.Signal and QtCore.Slot .
- The third thing is loading Ui files.
