Python Qt Bindings
Choosing a Binding
Criteria PySide6 PyQt6
Maintainer Qt Company (official) Riverbank Computing
License LGPL v3 GPL v3 / commercial
Commercial use Free (LGPL) Requires commercial license
QML/Qt Quick support Excellent Good
Type stubs Built-in PyQt6-stubs (third-party)
pyqtSignal / Signal
Signal
pySignal
pyqtSlot / Slot
Slot
pyqtSlot
Availability pip pip
Default recommendation: PySide6 — official binding, LGPL, ships with complete type stubs, better QML tooling.
API Compatibility Layer
For code that must support both:
try: from PySide6.QtWidgets import QApplication, QPushButton from PySide6.QtCore import Signal, Slot PYSIDE6 = True except ImportError: from PyQt6.QtWidgets import QApplication, QPushButton from PyQt6.QtCore import pyqtSignal as Signal, pyqtSlot as Slot PYSIDE6 = False
Or use qtpy — an abstraction layer maintained by the community:
from qtpy.QtWidgets import QApplication, QPushButton from qtpy.QtCore import Signal, Slot
Works with PySide6, PyQt6, PySide2, PyQt5 — set QT_API env var to select
PySide6 vs PyQt6: Key Differences
Signals and Slots
PySide6
from PySide6.QtCore import Signal, Slot class Foo(QObject): my_signal = Signal(int)
@Slot(int)
def my_slot(self, value: int): ...
PyQt6
from PyQt6.QtCore import pyqtSignal, pyqtSlot class Foo(QObject): my_signal = pyqtSignal(int)
@pyqtSlot(int)
def my_slot(self, value: int): ...
Enum Access
Both require fully-qualified enum access (breaking change from Qt5):
CORRECT (both bindings)
Qt.AlignmentFlag.AlignLeft QSizePolicy.Policy.Expanding QPushButton.setCheckable(True)
WRONG — Qt5 style (no longer works)
Qt.AlignLeft
Exec Method (PyQt6 breaking change)
PySide6
app.exec() dialog.exec()
PyQt6 — exec() also works in PyQt6 (exec_ removed)
app.exec() dialog.exec()
Both use exec() — the old exec_() workaround is no longer needed or available in PyQt6.
Property Decorator
PySide6
from PySide6.QtCore import Property @Property(int, notify=value_changed) def value(self) -> int: return self._value
PyQt6
from PyQt6.QtCore import pyqtProperty @pyqtProperty(int, notify=value_changed) def value(self) -> int: return self._value
Migrating PyQt5 → PySide6
Step 1: Update imports
Mass replace with sed
sed -i 's/from PyQt5./from PySide6./g' src//*.py sed -i 's/import PyQt5./import PySide6./g' src//*.py
Step 2: Replace signal/slot decorators
PyQt5 → PySide6
pyqtSignal → Signal pyqtSlot → Slot pyqtProperty → Property
Step 3: Fix enum usage (most common PyQt5→PySide6 breakage)
PyQt5 (short form)
Qt.AlignLeft → Qt.AlignmentFlag.AlignLeft Qt.Horizontal → Qt.Orientation.Horizontal QSizePolicy.Expanding → QSizePolicy.Policy.Expanding Qt.WindowModal → Qt.WindowModality.WindowModal
Step 4: Fix exec() calls — remove exec_() suffix:
app.exec_() → app.exec() dialog.exec_() → dialog.exec()
Step 5: Remove deprecated Qt5 API
Removed in Qt6
QWidget.show() — still works QApplication.setDesktopSettingsAware() — removed QFontDatabase.addApplicationFont() — still works
Migrating PyQt5 → PyQt6
Same steps as PySide6 migration, but:
PyQt5 → PyQt6 signals (keep pyqt prefix)
pyqtSignal → pyqtSignal (unchanged) pyqtSlot → pyqtSlot (unchanged)
Imports change
from PyQt5.QtWidgets import ... → from PyQt6.QtWidgets import ...
Enum changes are identical to PySide6 — both Qt6 bindings enforce fully-qualified enums.
Migrating PySide2 → PySide6
Imports
from PySide2. → from PySide6.
exec_ removal
.exec_() → .exec()
Enum qualification (same as PyQt5→PySide6)
PySide6 also drops Python 3.6/3.7 support — minimum is Python 3.8 (3.11 recommended).
Type Stubs
PySide6 ships stubs — no extra install
pip install PySide6
PyQt6
pip install PyQt6-stubs
Configure pyright/mypy
pyproject.toml
[tool.pyright] pythonVersion = "3.11"