Python PyQt program - Temperature converter

Last update on April 25 2025 12:56:14 (UTC/GMT +8 hours)

Write a Python program that implements a temperature converter app that lets users choose between Celsius and Fahrenheit using PyQt. Customize the widget appearance based on the selected unit.

From doc.qt.io:

QApplication Class: The QApplication class manages the GUI application's control flow and main settings.

QMainWindow Class: The QMainWindow class provides a main application window.

QWidget: The QWidget class is the base class of all user interface objects.

QVBoxLayout Class: The QVBoxLayout class lines up widgets vertically.

QLabel Class: The QLabel widget provides a text or image display.

QLineEdit Class: A line edit allows the user to enter and edit a single line of plain text with a useful collection of editing functions, including undo and redo, cut and paste, and drag and drop.

QPushButton: The push button, or command button, is perhaps the most commonly used widget in any graphical user interface. Push (click) a button to command the computer to perform some action, or to answer a question. Typical buttons are OK, Apply, Cancel, Close, Yes, No and Help.

QRadioButton: A QRadioButton is an option button that can be switched on (checked) or off (unchecked). Radio buttons typically present the user with a "one of many" choice. In a group of radio buttons, only one radio button at a time can be checked; if the user selects another button, the previously selected button is switched off.

Sample Solution:

Python Code:

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QWidget, QVBoxLayout, QLabel, QLineEdit, QPushButton, QRadioButton
class TemperatureConverterApp(QMainWindow):
    def __init__(self):
        super().__init__()

        # Set the window properties (title and initial size)
        self.setWindowTitle("Temperature Converter")
        self.setGeometry(100, 100, 300, 200)  # (x, y, width, height)

        # Create a central widget for the main window
        central_widget = QWidget()
        self.setCentralWidget(central_widget)

        # Create radio buttons for unit selection
        self.celsius_radio = QRadioButton("Celsius")
        self.fahrenheit_radio = QRadioButton("Fahrenheit")

        # Create labels and input fields for temperature input and result
        input_label = QLabel("Enter Temperature:")
        self.input_field = QLineEdit()
        result_label = QLabel("Result:")
        self.result_field = QLineEdit()
        self.result_field.setReadOnly(True)

        # Create a convert button
        convert_button = QPushButton("Convert")
        convert_button.clicked.connect(self.convert_temperature)

        # Create layout for unit selection
        unit_layout = QVBoxLayout()
        unit_layout.addWidget(self.celsius_radio)
        unit_layout.addWidget(self.fahrenheit_radio)

        # Create layout for temperature input and result
        input_layout = QVBoxLayout()
        input_layout.addWidget(input_label)
        input_layout.addWidget(self.input_field)
        input_layout.addWidget(result_label)
        input_layout.addWidget(self.result_field)
        input_layout.addWidget(convert_button)

        # Create layout for central widget
        layout = QVBoxLayout()
        layout.addLayout(unit_layout)
        layout.addLayout(input_layout)

        # Set the layout for the central widget
        central_widget.setLayout(layout)

        # Set default unit to Celsius
        self.celsius_radio.setChecked(True)
        self.fahrenheit_radio.setChecked(False)

    def convert_temperature(self):
        try:
            temperature = float(self.input_field.text())
            if self.celsius_radio.isChecked():
                # Convert from Celsius to Fahrenheit
                converted_temperature = (temperature * 9/5) + 32
                self.result_field.setText(f"{converted_temperature} °F")
            else:
                # Convert from Fahrenheit to Celsius
                converted_temperature = (temperature - 32) * 5/9
                self.result_field.setText(f"{converted_temperature} °C")
        except ValueError:
            self.result_field.setText("Invalid input")

def main():
    app = QApplication(sys.argv)
    window = TemperatureConverterApp()
    window.show()
    sys.exit(app.exec_())

if __name__ == "__main__":
    main()

Explanation:

In the exercise above -

Import the necessary modules.
Create a "QMainWindow" named "TemperatureConverterApp" with a central widget.
Set the window's title and initial size.
Create radio buttons (celsius_radio and fahrenheit_radio) for selecting the temperature unit (Celsius or Fahrenheit).
Create labels and input fields for temperature input (input_field) and display the result (result_field).
Create a "Convert" button and connect its click event to the "convert_temperature()" method.
Create layouts to arrange widgets, including unit selection and temperature input/result.
The "convert_temperature()" method converts the input temperature between Celsius and Fahrenheit based on the selected unit and updates the result field accordingly.
In the main function, we create the PyQt application, create an instance of the "TemperatureConverterApp" class, show the window, and run the application's event loop.

Output:

Flowchart:

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