Проблема с перетаскиванием, Drag-and-drop

Подскажите, как прописать условие, что если объект "бросается" в запретной зоне,
то он должен вернуться на свое место в исходном списке?

Ниже приведен полный код.

from PyQt6.QtCore import QMimeData, Qt, pyqtSignal
from PyQt6.QtGui import QDrag, QPixmap
from PyQt6.QtWidgets import (QApplication, QHBoxLayout,
    QLabel, QMainWindow, QVBoxLayout, QWidget,)


class DragTargetIndicator(QLabel):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.setContentsMargins(25, 5, 25, 5)
        self.setStyleSheet(
            "QLabel { background-color: #ccc; border: 1px solid black; }"
        )


class DragItem(QLabel):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.setContentsMargins(25, 5, 25, 5)
        self.setAlignment(Qt.AlignmentFlag.AlignCenter)
        self.setStyleSheet("border: 1px solid black;")
        # Store data separately from display label, but use label for default.
        self.data = self.text()

    def set_data(self, data):
        self.data = data

    def mouseMoveEvent(self, e):
        if e.buttons() == Qt.MouseButton.LeftButton:
            drag = QDrag(self)
            mime = QMimeData()
            drag.setMimeData(mime)

            pixmap = QPixmap(self.size())
            self.render(pixmap)
            drag.setPixmap(pixmap)

            drag.exec(Qt.DropAction.MoveAction)


class DragWidget(QWidget):
    orderChanged = pyqtSignal(list)

    def __init__(self, *args, orientation=Qt.Orientation.Vertical, **kwargs):
        super().__init__()
        self.setAcceptDrops(True)

        self.orientation = orientation

        if self.orientation == Qt.Orientation.Vertical:
            self.blayout = QVBoxLayout()
        else:
            self.blayout = QHBoxLayout()

        self._drag_target_indicator = DragTargetIndicator()
        self.blayout.addWidget(self._drag_target_indicator)
        self._drag_target_indicator.hide()

        self.setLayout(self.blayout)

    def dragEnterEvent(self, e):
        e.accept()

    def dragLeaveEvent(self, e):
        self._drag_target_indicator.hide()
        e.accept()

    def dragMoveEvent(self, e):
        # Find the correct location of the drop target, so we can move it there.
        index = self._find_drop_location(e)
        if index is not None:
            # Inserting moves the item if its alreaady in the layout.
            self.blayout.insertWidget(index, self._drag_target_indicator)
            # Hide the item being dragged.
            e.source().hide()
            # Show the target.
            self._drag_target_indicator.show()
        e.accept()

    def dropEvent(self, e):
        widget = e.source()
        # Use drop target location for destination, then remove it.
        self._drag_target_indicator.hide()
        index = self.blayout.indexOf(self._drag_target_indicator)
        if index is not None:
            self.blayout.insertWidget(index, widget)
            self.orderChanged.emit(self.get_item_data())
            widget.show()
            self.blayout.activate()
        e.accept()

    def _find_drop_location(self, e):
        pos = e.position()
        spacing = self.blayout.spacing() / 2

        for n in range(self.blayout.count()):
            # Get the widget at each index in turn.
            w = self.blayout.itemAt(n).widget()

            if self.orientation == Qt.Orientation.Vertical:
                # Drag drop vertically.
                drop_here = (
                    pos.y() >= w.y() - spacing
                    and pos.y() <= w.y() + w.size().height() + spacing
                )
            else:
                # Drag drop horizontally.
                drop_here = (
                    pos.x() >= w.x() - spacing
                    and pos.x() <= w.x() + w.size().width() + spacing
                )

            if drop_here:
                # Drop over this target.
                break

        return n

    def add_item(self, item):
        self.blayout.addWidget(item)

    def get_item_data(self):
        data = []
        for n in range(self.blayout.count()):
            # Get the widget at each index in turn.
            w = self.blayout.itemAt(n).widget()
            if w != self._drag_target_indicator:
                # The target indicator has no data.
                data.append(w.data)
        return data


class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.drag = DragWidget(orientation=Qt.Orientation.Vertical)
        for n, l in enumerate(["A", "B", "C", "D"]):
            item = DragItem(l)
            item.set_data(n)  # Store the data.
            self.drag.add_item(item)

        self.drag.orderChanged.connect(print)

        container = QWidget()
        layout = QVBoxLayout()
        layout.addStretch(1)
        layout.addWidget(self.drag)
        layout.addStretch(1)
        container.setLayout(layout)

        self.setCentralWidget(container)


app = QApplication([])
w = MainWindow()
w.show()
app.exec()