How to make the picture zoom (QGraphicsItem), and make scrollbars change their size accordingly (QGraphicsScene)?

How do I scale the drawn pixmap of QGraphicsItem? Can't find any setScaled(), size or height property there. After the picture becomes big, the scrollbars of MyGraphicsView class should be able to scroll the big scaled picture.

#!/usr/bin/env python

from PyQt5.QtCore import (QRectF, Qt)
from PyQt5.QtGui import (QPainter, QPixmap)
from PyQt5.QtWidgets import (QMainWindow, QApplication, QGraphicsView, QGraphicsScene, QGraphicsItem)


class TicTacToe(QGraphicsItem):
    def __init__(self, helper):
        super(TicTacToe, self).__init__()
        self.mypixmap = QPixmap("exit.png")

    def paint(self, painter, option, widget):
        painter.setOpacity(1)
        painter.drawPixmap(0,0, 300, 300, self.mypixmap)


    def boundingRect(self):
        return QRectF(0,0,300,300)


class MyGraphicsView(QGraphicsView):
    def __init__(self):
        super(MyGraphicsView, self).__init__()
        scene = QGraphicsScene(self)

        self.tic_tac_toe = TicTacToe(self)

        scene.addItem(self.tic_tac_toe)

        self.setScene(scene)

        self.setHorizontalScrollBarPolicy(Qt.ScrollBarAlwaysOn)
        self.setVerticalScrollBarPolicy(Qt.ScrollBarAlwaysOn)


class Example(QMainWindow):    
    def __init__(self):
        super(Example, self).__init__()

        self.y = MyGraphicsView()
        self.setCentralWidget(self.y)

if __name__ == '__main__':
    import sys
    app = QApplication(sys.argv)
    w = Example()
    w.show()
    sys.exit(app.exec_())