Introduction to PyQt5

PyQt5 is one of the most popular Python libraries for creating cross-platform GUI (Graphical User Interface) applications. It combines the power of Python and Qt, a robust C++ framework, enabling developers to create highly responsive and visually appealing desktop applications. With dozens of APIs and tools, PyQt5 provides complete control over GUI elements, events, and advanced features such as multimedia, threading, and database integration.

Key Features and APIs in PyQt5

1. QApplication

The QApplication class is essential for every PyQt5 application. It initializes the application and handles event loops.

  from PyQt5.QtWidgets import QApplication
  import sys

  app = QApplication(sys.argv)
  print("PyQt5 application is running!")
  sys.exit(app.exec_())

2. QMainWindow

This class provides the main application window, including support for menus, toolbars, and a status bar.

  from PyQt5.QtWidgets import QApplication, QMainWindow
  import sys

  class MainWindow(QMainWindow):
      def __init__(self):
          super().__init__()
          self.setWindowTitle('PyQt5 Main Window')
          self.setGeometry(100, 100, 800, 600)

  app = QApplication(sys.argv)
  window = MainWindow()
  window.show()
  sys.exit(app.exec_())

3. QWidget

The QWidget is a generic container for GUI controls and serves as a base class for other UI components.

  from PyQt5.QtWidgets import QApplication, QWidget, QLabel
  import sys

  app = QApplication(sys.argv)
  window = QWidget()
  window.setWindowTitle('QWidget Example')
  window.setGeometry(100, 100, 300, 200)

  label = QLabel('Hello, PyQt5!', window)
  label.move(50, 50)

  window.show()
  sys.exit(app.exec_())

4. QPushButton

The QPushButton is a button element for user interaction. Below is an example demonstrating its usage:

  from PyQt5.QtWidgets import QApplication, QWidget, QPushButton
  import sys

  def on_click():
      print('Button clicked!')

  app = QApplication(sys.argv)
  window = QWidget()
  window.setWindowTitle('QPushButton Example')
  window.setGeometry(100, 100, 300, 200)

  button = QPushButton('Click Me', window)
  button.clicked.connect(on_click)
  button.move(100, 100)

  window.show()
  sys.exit(app.exec_())

5. QLineEdit

QLineEdit is a control for single-line text input.

  from PyQt5.QtWidgets import QApplication, QWidget, QLineEdit
  import sys

  app = QApplication(sys.argv)
  window = QWidget()
  window.setWindowTitle('QLineEdit Example')
  window.setGeometry(100, 100, 400, 200)

  line_edit = QLineEdit(window)
  line_edit.setPlaceholderText('Enter some text...')
  line_edit.move(50, 50)

  window.show()
  sys.exit(app.exec_())

6. QMessageBox

This offers a pre-configured dialog box used to show messages or obtain user decisions.

  from PyQt5.QtWidgets import QApplication, QMessageBox
  import sys

  app = QApplication(sys.argv)
  msg_box = QMessageBox()
  msg_box.setText('Are you sure you want to continue?')
  msg_box.setWindowTitle('Confirmation')
  msg_box.exec_()

7. QFileDialog

The QFileDialog allows users to browse and select files or directories.

  from PyQt5.QtWidgets import QApplication, QFileDialog
  import sys

  app = QApplication(sys.argv)
  file_name, _ = QFileDialog.getOpenFileName(None, 'Select File', '', 'All Files (*)')
  print('Selected File:', file_name)

8. QVBoxLayout and QHBoxLayout

These layout managers help in organizing widgets vertically or horizontally.

  from PyQt5.QtWidgets import QApplication, QWidget, QVBoxLayout, QPushButton
  import sys

  app = QApplication(sys.argv)
  window = QWidget()
  window.setWindowTitle('Layouts in PyQt5')

  layout = QVBoxLayout()
  button1 = QPushButton('Button 1')
  button2 = QPushButton('Button 2')
  layout.addWidget(button1)
  layout.addWidget(button2)

  window.setLayout(layout)
  window.show()
  sys.exit(app.exec_())

Complete Example: A Simple To-Do App

Below is an example of a minimal to-do application using some of the APIs discussed above.

  from PyQt5.QtWidgets import QApplication, QWidget, QVBoxLayout, QLineEdit, QPushButton, QListWidget
  import sys

  def add_task():
      task = task_input.text()
      if task:
          task_list.addItem(task)
          task_input.clear()

  app = QApplication(sys.argv)
  window = QWidget()
  window.setWindowTitle('To-Do App')

  layout = QVBoxLayout()
  task_input = QLineEdit()
  task_input.setPlaceholderText('Enter a new task...')
  add_button = QPushButton('Add Task')
  add_button.clicked.connect(add_task)
  task_list = QListWidget()

  layout.addWidget(task_input)
  layout.addWidget(add_button)
  layout.addWidget(task_list)
  window.setLayout(layout)

  window.show()
  sys.exit(app.exec_())

Conclusion

PyQt5 is a powerful tool for building desktop applications, providing a rich set of APIs and tools that simplify application development. By mastering its core components such as QApplication, QWidget, and layout managers, you can unleash its full potential and create both simple and complex applications efficiently.