dnd_problem.py

import sys

from PyQt4 import QtCore, QtGui


class MyDraggableWidget(QtGui.QLabel):
    def __init__(self):
        QtGui.QLabel.__init__(self)
        self.setText("DRAG ME")

        self._startpos = None

    def mousePressEvent(self, event):
        self._startpos = QtCore.QPoint(event.pos())
        QtGui.QLabel.mousePressEvent(self, event)

    def mouseMoveEvent(self, event):
        p = event.pos() - self._startpos
        if p.manhattanLength() >= QtGui.QApplication.startDragDistance():
            drag = QtGui.QDrag(self)
            mimeData = QtCore.QMimeData()
            mimeData.widget = self
            drag.setMimeData(mimeData)
            drag.exec_(QtCore.Qt.MoveAction)


class MyTargetWidget(QtGui.QWidget):
    def __init__(self):
        QtGui.QWidget.__init__(self)
        self.setMinimumSize(80, 80)
        self.setAcceptDrops(True)

    def paintEvent(self, event):
        QtGui.QWidget.paintEvent(self, event)
        painter = QtGui.QPainter(self)
        painter.setPen(QtGui.QColor(255, 0, 0))
        painter.drawLine(0, 0, self.width(), self.height())
        painter.drawLine(15, self.height(), self.width() - 15, 0)

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

    def dropEvent(self, event):
        mimeData = event.mimeData()
        event.accept()
        mimeData.widget.deleteLater() # OMG


if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)

    window = QtGui.QWidget()
    layout = QtGui.QVBoxLayout()
    draggable = MyDraggableWidget()
    layout.addWidget(draggable)
    target = MyTargetWidget()
    layout.addWidget(target)
    window.setLayout(layout)

    window.setVisible(True)

    app.exec_()