PyQt6

6.11.0 · active · verified Thu Apr 09

PyQt6 provides Python bindings for the Qt cross-platform application development framework, allowing developers to create desktop applications with native look and feel. It is currently at version 6.11.0 and typically releases new versions in close alignment with the major and minor releases of the underlying Qt library.

Warnings

breaking Enum values (like `Qt.AlignRight`) must now be accessed via explicit enum types (e.g., `Qt.AlignmentFlag.AlignRight`, `Qt.ItemFlag.Selectable`). Direct access via `Qt.` is deprecated or removed in PyQt6.
Fix: Update all enum references to use the specific enum class (e.g., `Qt.AlignmentFlag.AlignCenter` instead of `Qt.AlignCenter`). Refer to the PyQt6 documentation for the correct enum types.
breaking The `QApplication` instance must be a singleton. Attempting to create a second `QApplication` will raise a `RuntimeError` (`RuntimeError: Application.instance() must be called before QApplication constructor`).
Fix: Ensure `QApplication` is instantiated only once. In test environments or complex applications, check for an existing instance using `QApplication.instance()` before creating a new one: `app = QApplication.instance() or QApplication(sys.argv)`.
gotcha Performing long-running or blocking operations directly on the main GUI thread will freeze your application's user interface, making it unresponsive.
Fix: Offload intensive computations or I/O operations to separate threads using `QThread` or Python's `threading`/`multiprocessing` modules. Use Qt's signal/slot mechanism to communicate results back to the GUI thread for UI updates.
gotcha PyQt6 (Qt) objects have a parent-child ownership model. If an object has a parent, it is automatically deleted when its parent is deleted. Misunderstanding this can lead to memory leaks (orphaned objects without parents) or premature object deletion.
Fix: Always assign a parent to widgets where appropriate (e.g., `QLabel('Text', parent=self)`). For objects without a parent, explicitly manage their lifecycle or ensure they are properly referenced to prevent Python's garbage collector from deleting them prematurely if they are still needed by Qt.

Install

pip install PyQt6 Install PyQt6

Imports

QApplication

from PyQt6.QtWidgets import QApplication

QWidget
```
from PyQt6.QtWidgets import QWidget
```
QLabel
```
from PyQt6.QtWidgets import QLabel
```
QVBoxLayout
```
from PyQt6.QtWidgets import QVBoxLayout
```
Qt
```
from PyQt6.QtCore import Qt
```
While some Qt enums were accessible via QtWidgets in PyQt5, PyQt6 enforces stricter module separation. Core enums like AlignmentFlag are in QtCore.

Quickstart

This quickstart creates a simple desktop application window with a 'Hello, PyQt6!' label centered within it. It demonstrates the basic structure of a PyQt6 application, including `QApplication` instantiation, creating a `QWidget`, using a layout, and running the event loop.

import sys
from PyQt6.QtWidgets import QApplication, QWidget, QLabel, QVBoxLayout
from PyQt6.QtCore import Qt

class MyWindow(QWidget):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("My PyQt6 App")
        self.setGeometry(100, 100, 400, 200)

        layout = QVBoxLayout()
        label = QLabel("Hello, PyQt6!", self)
        label.setAlignment(Qt.AlignmentFlag.AlignCenter)
        layout.addWidget(label)
        self.setLayout(layout)

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

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