import sys
from PyQt5.QtWidgets import QApplication, QWidget, QFrame
from PyQt5.QtGui import QColor, QPainter, QImage
from PyQt5.QtCore import Qt
class Example(QWidget):
    def __init__(self):
        super().__init__()
        self.initUI()
    def initUI(self):
        self.resize(500,500)
        self.frame = QFrame(self)
        self.frame.resize(400,200)
        self.frame.move(50,200)
        self.frame.setStyleSheet('QWidget {Background-color: %s}'% QColor('white').name())
        self.image = QImage(200,200, QImage().Format_ARGB32)
        self.paint = QPainter(self.image)
        self.show()
    def paintEvent(self, e):
        paint = QPainter(self.frame)
        paint.drawImage(0,0,self.image)
    def mousePressEvent(self, e):
        if e.button() == Qt.LeftButton:
            self.goEllipse(e)
    def mouseMoveEvent(self, e):
        self.goEllipse(e)
    def goEllipse(self, e):
        self.paint.setBrush(QColor('black'))
        self.paint.drawEllipse(e.pos(), 10, 10)
        self.frame.update()
app = QApplication(sys.argv)
w = Example()
sys.exit(app.exec_())

 import sys
from PyQt5.QtWidgets import *
from PyQt5.QtGui import *
from PyQt5.QtCore import Qt
    
class Frame(QFrame):
    def __init__(self,parent=None):
        QFrame.__init__(self,parent)
        self.resize(400,200)
        self.setStyleSheet('QWidget {Background-color: %s}'% QColor('white').name())
        self.pix = QPixmap(400,200)
        self.pix.fill(QColor(0,0,0,0))
    def paintEvent(self, e):
        p = QPainter(self)
        p.drawPixmap(0,0,self.pix)
    def mousePressEvent(self, e):
        if e.button() == Qt.LeftButton:
            self.goEllipse(e)
    def mouseMoveEvent(self, e):
        self.goEllipse(e)
    def goEllipse(self, e):
        p = QPainter(self.pix)
        p.setBrush(QColor('green'))
        p.drawEllipse(e.pos(), 10, 10)
        self.update()
class W(QWidget):
    def __init__(self,parent=None):
        QWidget.__init__(self,parent)
        self.frame = Frame(self)
        self.frame.move(50,200)
        
app = QApplication(sys.argv)
w = W()
w.resize(500,500)
w.show()
sys.exit(app.exec_())