Simple QDial subclass with paint event override

simpledial.py

from PyQt5 import QtCore, QtGui, QtWidgets

class SimpleDial(QtWidgets.QDial):
    def paintEvent(self, event):
        # create a QStyleOption for the dial, and initialize it with the basic properties
        # that will be used for the configuration of the painter
        opt = QtWidgets.QStyleOptionSlider()
        self.initStyleOption(opt)

        # construct a QRectF that uses the minimum between width and height, 
        # and adds some margins for better visual separation
        # this is partially taken from the fusion style helper source
        width = opt.rect.width()
        height = opt.rect.height()
        r = min(width, height) / 2
        r -= r / 50
        d_ = r / 6
        dx = opt.rect.x() + d_ + (width - 2 * r) / 2 + 1
        dy = opt.rect.y() + d_ + (height - 2 * r) / 2 + 1
        br = QtCore.QRectF(dx + .5, dy + .5, 
            int(r * 2 - 2 * d_ - 2), 
            int(r * 2 - 2 * d_ - 2))

        penColor = self.palette().dark().color()
        qp = QtGui.QPainter(self)
        qp.setRenderHints(qp.Antialiasing)
        qp.setPen(QtGui.QPen(penColor, 4))
        qp.drawEllipse(br)

        # find the "real" value ratio between minimum and maximum
        realValue = (self.value() - self.minimum()) / (self.maximum() - self.minimum())
        # compute the angle at which the dial handle should be placed, assuming
        # a range between 240° and 300° (moving clockwise)
        angle = 240 - 300 * realValue
        # create a polar line for the position of the handle; this can also
        # be done using the math module with some performance improvement
        line = QtCore.QLineF.fromPolar(r * .6, angle)
        line.translate(br.center())
        ds = r / 5
        # create the handle rect and position it at the end of the polar line
        handleRect = QtCore.QRectF(0, 0, ds, ds)
        handleRect.moveCenter(line.p2())
        qp.setPen(QtGui.QPen(penColor, 2))
        qp.drawEllipse(handleRect)


if __name__ == '__main__':
    import sys
    app = QtWidgets.QApplication(sys.argv)
    dial = SimpleDial()
    dial.show()
    sys.exit(app.exec_())