import sys

from PyQt5 import QtWidgets, QtGui


class MainWindow(QtWidgets.QMainWindow):

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

        self.label = QtWidgets.QLabel()
        canvas = QtGui.QPixmap(400, 300)
        self.label.setPixmap(canvas)
        self.setCentralWidget(self.label)
        self.draw_something()

    def draw_something(self):
        painter = QtGui.QPainter(self.label.pixmap())
        pen = QtGui.QPen()
        pen.setWidth(3)
        pen.setColor(QtGui.QColor(204, 0, 0))  # r, g, b
        painter.setPen(pen)

        painter.drawEllipse(10, 10, 100, 100)
        painter.drawEllipse(10, 10, 150, 200)
        painter.drawEllipse(10, 10, 200, 300)
        painter.end()


if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    window = MainWindow()
    window.show()
    app.exec_()