title: How to use QPainter in a QWidget in PyQt4
body: <p>My code below currently opens a 500x500 QMainWindow that is blank.</p>
  
  <p>I am simply trying to draw a circle in the QWidget using QPainter.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>from PyQt4 import QtCore, QtGui, Qt
  from PyQt4.QtGui import QApplication, QMainWindow
  import sys
  
  
  class Ui_MainWindow(object):
      def setupUi(self, MainWindow):
          MainWindow.resize(500, 500)
          self.centralwidget = QtGui.QWidget(MainWindow)
          self.horizontalLayout = QtGui.QHBoxLayout(self.centralwidget)
          MainWindow.setCentralWidget(self.centralwidget)
          self.menubar = QtGui.QMenuBar(MainWindow)
          self.menubar.setGeometry(QtCore.QRect(0, 0, 500, 22))
          MainWindow.setMenuBar(self.menubar)
          self.statusbar = QtGui.QStatusBar(MainWindow)
          MainWindow.setStatusBar(self.statusbar)
          QtCore.QMetaObject.connectSlotsByName(MainWindow)
  
  class MyMainScreen(QMainWindow):
      def __init__(self, parent=None):
          QtGui.QMainWindow.__init__(self, parent)
          self.ui = Ui_MainWindow()  # This is from a python export from QtDesigner
          self.ui.setupUi(self)
  
          self.paintCircle()
  
  
      def paintCircle(self):
          self.painter = QtGui.QPainter(self)
          self.painter.begin(self)
          self.painter.setPen(Qt.QPen(Qt.QColor.black))
          # painter.end()
          self.painter.drawArc(QtCore.QRectF(250, 250, 10, 10), 0, 5760)
  
  
  if __name__ == "__main__":
      app = QApplication(sys.argv)
      mainscreen = MyMainScreen()
      mainscreen.show()
      app.exec_()
  </code></pre>
  
  <p>I'm getting the following errors:</p>
  
  <pre><code>QPainter::begin: Paint device returned engine == 0, type: 1
  QPainter::begin: Paint device returned engine == 0, type: 1
  QPainter::setPen: Painter not active
  </code></pre>