PySide6 Code Reviewer

Expert code review for modern PySide6/Qt 6.8+ applications.

Review Process

• Identify Qt version assumptions — Verify code targets Qt 6.8+ (no Qt5 compat)

• Check thread safety — All GUI operations on main thread, proper worker patterns

• Validate signal/slot usage — Modern connection syntax, proper signatures

• Assess Model/View implementation — Role usage, data method patterns, index validity

• Review resource management — Parent-child ownership, prevent leaks

• Evaluate async patterns — QThread, QtConcurrent, asyncio integration

• Check QML integration — Property bindings, type registration, context exposure

Critical Anti-Patterns (Always Flag)

WRONG: GUI operation from worker thread

class Worker(QThread): def run(self): self.label.setText("Done") # CRASH: Cross-thread GUI access

WRONG: Blocking the event loop

def on_button_click(self): time.sleep(5) # FREEZES UI requests.get(url) # FREEZES UI

WRONG: Old-style signal connection (Qt4/5 legacy)

self.connect(button, SIGNAL("clicked()"), self.handler)

WRONG: String-based slot connection

button.clicked.connect("self.handler") # Should be callable

WRONG: No parent = memory leak risk

label = QLabel("text") # Should have parent or be assigned to layout

WRONG: Deleting QObject while signals pending

obj.deleteLater() # OK del obj # WRONG if signals/slots active

WRONG: Direct widget manipulation in QThread.run()

class BadWorker(QThread): def run(self): self.progress_bar.setValue(50) # Thread violation!

Modern Patterns (Require These)

Signal/Slot Connections

Qt 6 style - always use this

button.clicked.connect(self.on_click) button.clicked.connect(lambda: self.handler(arg))

Typed signals with modern syntax

class Worker(QObject): progress = Signal(int) # Single type result = Signal(str, list) # Multiple types error = Signal(Exception) # Exception passing finished = Signal() # No arguments

Thread-Safe Worker Pattern

class Worker(QObject): finished = Signal() progress = Signal(int) result = Signal(object) error = Signal(str)

@Slot()
def run(self):
    try:
        for i in range(100):
            # Do work
            self.progress.emit(i)
        self.result.emit(data)
    except Exception as e:
        self.error.emit(str(e))
    finally:
        self.finished.emit()

Usage

thread = QThread() worker = Worker() worker.moveToThread(thread) thread.started.connect(worker.run) worker.finished.connect(thread.quit) worker.finished.connect(worker.deleteLater) thread.finished.connect(thread.deleteLater) thread.start()

Async Integration (Qt 6.8+)

import asyncio from PySide6.QtAsyncio import QAsyncioEventLoopPolicy

Set up asyncio with Qt event loop

asyncio.set_event_loop_policy(QAsyncioEventLoopPolicy())

class AsyncWidget(QWidget): async def fetch_data(self): async with aiohttp.ClientSession() as session: async with session.get(url) as response: return await response.json()

def start_fetch(self):
    asyncio.ensure_future(self.fetch_data())

Detailed Reference Files

• references/signals-slots.md — Signal/slot patterns, connection types, thread-safe emission

• references/model-view.md — QAbstractItemModel, roles, proxies, delegates

• references/threading.md — QThread, QtConcurrent, async patterns, thread pools

• references/widgets.md — Widget lifecycle, layouts, styling, high-DPI

• references/qml-integration.md — QML/Python bridge, properties, type registration

• references/performance.md — Paint optimization, model efficiency, lazy loading

• references/anti-patterns.md — Comprehensive anti-pattern catalog with fixes

Review Checklist (Use for PRs)

Thread Safety

• All widget/GUI calls on main thread only

• Workers use signal/slot for UI updates

• No time.sleep() or blocking calls in main thread

• QThread subclass only overrides run() , not constructor work

• moveToThread() used correctly (object has no parent)

Memory Management

• Widgets have parents OR are added to layouts

• deleteLater() used for QObjects, never del

• Lambda connections don't capture stale references

• Circular signal connections avoided

• Model data returned by value, not reference

Signal/Slot Correctness

• Modern connection syntax (no strings)

• Signal signatures match slot signatures

• @Slot() decorator on all slots

• Qt.QueuedConnection for cross-thread signals

• Signals defined as class attributes

Model/View

• beginInsertRows() /endInsertRows() bracket changes

• dataChanged emitted for updates

• index.isValid() checked before access

• Custom roles use Qt.UserRole + n

• roleNames() override for QML compatibility

Performance

• No widget creation in paint events

• update() not repaint() for redraws

• Large lists use QAbstractItemModel (not QListWidget)

• Lazy loading for expensive data

• blockSignals() during batch updates

Qt 6.8+ Specifics

• Using new enum scoping (Qt.AlignmentFlag.AlignCenter )

• QtAsyncio for async patterns (not third-party)

• QML_ELEMENT macro equivalents for type registration

• Property bindings via QProperty where appropriate

• New QPermission API for platform permissions