问通过鼠标事件PyQt在PyQt窗口中创建一行

EN

import sys, random
from PyQt4 import QtGui, QtCore

class P(QtGui.QWidget):

    def __init__(self):
        super(P, self).__init__()

        self.initUI()

    def initUI(self):
        q=self.frameGeometry()
        cp=QtGui.QDesktopWidget().availableGeometry().center()
        q.moveCenter(cp)
        self.setFixedSize(300,300)
        self.setWindowTitle('Points')
        self.show()

    def mousePressEvent(self, QMouseEvent):
        cursor =QtGui.QCursor(self)
        position = QMouseEvent.pos()
        xpos = QMouseEvent.x()
        ypos = QMouseEvent.y()

        #Trial ??????
        q = QtGui.QPainter()
        q.drawLine(30,30,90,90)

        print QMouseEvent.pos()

    def mouseReleaseEvent(self, QMouseEvent):
        cursor =QtGui.QCursor()
        print cursor.pos()

    def paintEvent(self,e):
        qp = QtGui.QPainter()
        qp.begin(self)

        E1 = qp.drawEllipse(30,30,20,20)
        E2 = qp.drawEllipse(30,130,20,20)

def main():

    app = QtGui.QApplication(sys.argv)
    ex = P()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()