QWidget painter - qt

Question

I have this code:
import sys, random, pprint
from PyQt5 import QtWidgets, QtGui, QtCore
from PyQt5 import QtGui
from PyQt5.QtCore import Qt
class Window(QtWidgets.QMainWindow):
def __init__(self):
super().__init__()
self.initUI()
def initUI(self):
self.setGeometry(QtCore.QRect(200, 200, 700, 700))
self.widget = QtWidgets.QWidget(self)
self.widget.setGeometry(QtCore.QRect(10, 10, 400, 200))
self.widget.setObjectName("widget")
def paintEvent(self, event):
painter = QtGui.QPainter()
painter.begin(self.widget)
self.drawPoints(painter)
painter.end()
def drawPoints(self, painter):
#drawing code
if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
ex = Window()
ex.show()
sys.exit(app.exec_())
What do i expect: area (400x200) which would be painted by drawPoints(). QWidget inherits QPaintDevice. So this code should work. But console says:
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::end: Painter not active, aborted
Could you help me, please.

Answer 1

It looks like you are attempting to replicate this example, correct?
The major difference appears to be that you are defining paintEvent() for the main window, rather than the widget you are actually trying to paint. It would work if you created a custom subclass of QWidget, defined paintEvent() there, and then inserted that into a standard QMainWindow instance, like this:
class MyWidget(QtWidgets.QWidget):
def __init__(self, parent=None):
super(MyWidget, self).__init__(parent=parent)
self.initUI()
def initUI(self):
self.setGeometry(QtCore.QRect(10, 10, 400, 200))
self.setObjectName("widget")
def paintEvent(self, event):
painter = QtGui.QPainter()
painter.begin(self)
self.drawPoints(painter)
painter.end()
def drawPoints(self, painter):
pass
if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
my_window = QtWidgets.QMainWindow()
my_window.setGeometry(QtCore.QRect(200, 200, 700, 700))
my_window.setCentralWidget(MyWidget(my_window))
my_window.show()
sys.exit(app.exec_())
At the very least, it isn't printing that error message anymore.