QPixmap not updating in QGraphicsScene after using QPainter on it

[Leo_Red]

I created a custom widget modifies QPixmap which just adds QPianter drawing function to the widget.

from PySide2.QtGui import QPixmap
from PySide2.QtGui import QPainter
from ui import painter
class Surface(QPixmap):
    def __init__(self, *args):
        super().__init__(*args)
        self.Painter = QPainter(self)
    
    def drawRect(self,x,y,w,h):
        self.Painter.drawRect(x,y,w,h)

    def drawEllipse(self,x,y,w,h):
        self.Painter.drawEllipse(x,y,w,h)
    
    def drawLine(self,x1,y1,x2,y2):
        self.Painter.drawLine(x1,y1,x2,y2)

Here is the main.py (for testing)

from PySide2.QtWidgets import QApplication, QMainWindow, QPushButton, QGraphicsView, QGraphicsScene, QGraphicsPixmapItem
from PySide2.QtGui import QPixmap, QPainter
from ui import painter
from Surface import Surface
class Painter(QMainWindow):
    def __init__(self):
        super().__init__()
        self.ui = painter.Ui_MainWindow()
        self.ui.setupUi(self)
        
        self.scene = QGraphicsScene()
        self.ui.graphicsView.setScene(self.scene)
        self.pix = Surface('/home/midhil/Documents/Painter/src/hallo.png')
        self.ui.rectange.clicked.connect(self.drawRect)
        self.pixmapItem = QGraphicsPixmapItem(self.pix)
        self.scene.addItem()
    
    def drawRect(self):
        self.pix.drawRect(0,0,40,40)
        print("function called")
        
app = QApplication([])

window = Painter()
window.show()

app.exec_()

When the rectangle button is clicked, it draws a rect on the pixmap. But, the QGraphicsScene doesn't update. I tried update(), but it didn't work. What did work was readding the pixmap. But, I think it's inconvenient. Is there a proper way to solve this?