import sys
from PyQt5.QtWidgets import *

class Qscene(QGraphicsScene):

def __init__(self, parent=None):
   super(Qscene, self).__init__(parent)



def mousePressEvent(self, event):
    super(Qscene, self).mousePressEvent(event)

    self.xRect = event.scenePos().x()
    self.yRect = event.scenePos().y()


def mouseReleaseEvent(self, event):
    super(Qscene, self).mouseReleaseEvent(event)
    QGraphicsScene.addRect(self,self.xRect,self.yRect,self.endX-
    self.xRect,self.endY-self.yRect)

def mouseMoveEvent(self, event):
    super(Qscene, self).mouseMoveEvent(event)
    self.endX = event.scenePos().x()
    self.endY = event.scenePos().y()


if __name__ == '__main__':

app = QApplication(sys.argv)
window = QWidget()
scene = Qscene()
view = QGraphicsView()
view.setScene(scene)

hbox = QGridLayout()
hbox.addWidget(view)

window.setLayout(hbox)
window.show()

sys.exit(app.exec_())