PyQt5

Warnings

• breaking The `exec()` method on QApplication and QDialog instances was renamed to `exec_()` in PyQt5 (and earlier versions targeting Python 2) to avoid conflicts with Python's `exec` keyword. While `exec()` works in PyQt5 for Python 3, `exec_()` is the widely adopted and safer convention for PyQt5 applications. In PyQt6, it reverted to `exec()`.
  Fix: Always use `app.exec_()` for QApplication and dialogs in PyQt5 to ensure compatibility across various minor versions and to distinguish it from Python's keyword.
• gotcha Development tools like Qt Designer (`designer.exe`), `pyuic5`, and `pyrcc5` are no longer included directly with the `PyQt5` wheel installation. They are provided in a separate package, `pyqt5-tools`.
  Fix: Install `pyqt5-tools` separately: `pip install pyqt5-tools~=5.15`. You can then find `designer.exe` (or equivalent) in your virtual environment's `Scripts` (Windows) or `bin` (Linux/macOS) directory.
• breaking Migration from PyQt4 to PyQt5 involves significant breaking changes, notably the removal of the 'old-style' `QObject.connect()` signal/slot syntax and the re-organization of classes from the `QtGui` module into `QtGui`, `QtWidgets`, and `QtPrintSupport` modules.
  Fix: Update signal/slot connections to the 'new-style' Python callable syntax (e.g., `button.clicked.connect(self.my_slot)`). Adjust imports to reflect the new module structure for GUI elements.
• gotcha With the release of PyQt6 (targeting Qt6), PyQt5 is considered a mature but older generation. While PyQt5 is still actively maintained, new projects are often encouraged to start with PyQt6 for modern features, better performance, and long-term support. There are differences in enum naming (fully qualified names in PyQt6), module organization (e.g., `QAction` moved), and High DPI scaling defaults.
  Fix: For new projects, evaluate PyQt6. If sticking with PyQt5, be aware of migration paths and potential differences if examples/tutorials from PyQt6 are encountered. PyQt5 supports fully qualified enum names which helps with future compatibility.
• gotcha Official PyQt5 documentation often links to the C++ Qt documentation. This means users may need to infer Python equivalents from C++ signatures and concepts, which can be a learning curve for those unfamiliar with C++.
  Fix: Familiarize yourself with common C++ to Python binding patterns (e.g., `const QString&` in C++ often translates to `str` in Python). Utilize community tutorials and examples specific to PyQt5.

Install

• pip install PyQt5 Install PyQt5

Imports

• QApplication

  from PyQt5.QtWidgets import QApplication

• QWidget

  from PyQt5.QtWidgets import QWidget

• QLabel

  from PyQt5.QtWidgets import QLabel

• QPushButton

  from PyQt5.QtWidgets import QPushButton

• QVBoxLayout

  from PyQt5.QtWidgets import QVBoxLayout

• Qt

  from PyQt5.QtCore import Qt

  Qt core enums (like alignment flags, key codes) are typically found in QtCore.Qt, not QtGui.

Quickstart

This quickstart creates a simple PyQt5 window displaying 'Hello, PyQt5!' in a centrally aligned label. It demonstrates the basic structure of a PyQt5 application, including creating an QApplication instance, defining a main window (subclassing QWidget), adding a QLabel, setting layout, and starting the application's event loop.

import sys
from PyQt5.QtWidgets import QApplication, QWidget, QLabel, QVBoxLayout
from PyQt5.QtCore import Qt

class MyWindow(QWidget):
    def __init__(self):
        super().__init__()
        self.setWindowTitle('PyQt5 Hello World')
        self.setGeometry(100, 100, 400, 200) # x, y, width, height

        layout = QVBoxLayout()
        self.label = QLabel('Hello, PyQt5!', self)
        self.label.setAlignment(Qt.AlignCenter)
        self.label.setStyleSheet("font-size: 24px; color: blue;")

        layout.addWidget(self.label)
        self.setLayout(layout)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = MyWindow()
    window.show()
    sys.exit(app.exec_())