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I've run out of ideas and I need some help. Consider the following snippet (modified http://www.riverbankcomputing.com/pipermail/pyqt/2014-July/034542.html ):

from OpenGL import GL
from PyQt5 import Qt
class GLWindow(Qt.QWindow):
    def __init__(self):
        super().__init__()
        self.setSurfaceType(Qt.QWindow.OpenGLSurface)
        self.context = Qt.QOpenGLContext()
        self.context.setFormat(self.requestedFormat())
        if not self.context.create():
            raise Exception('self.context.create() failed')
        self.create()
    def exposeEvent(self, ev):
        ev.accept()
        if self.isExposed() and self.isVisible():
            self.update()
    def update(self):
        self.context.makeCurrent(self)
        GL.glClearColor(1.0, 0.0, 0.0, 0.0)
        GL.glClearDepth(1)
        GL.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT)
        GL.glFlush()
        self.context.swapBuffers(self)
app = Qt.QApplication([])
win = GLWindow()
widget = Qt.QWidget.createWindowContainer(win, None, Qt.Qt.Widget)
widget.show()
app.exec_()
No matter what OpenGL functions I call after makeCurrent(), they raise the following exception:
  File "errorchecker.pyx", line 53, in OpenGL_accelerate.errorchecker._ErrorChecker.glCheckError (src\errorchecker.c:1218)
OpenGL.error.GLError: GLError(
        err = 1282,
        description = b'nieprawid\xb3owa operacja',
        baseOperation = glClearColor,
        cArguments = (1.0, 0.0, 0.0, 0.0)
Besides, none of PyQt5 OpenGL examples, except openglwindow.py, work.
I'm using Python 3.4.2 win32, PyQt5 5.3.2 and PyOpenGL 3.1.0. Any ideas? I've found that PyQt5 binary was probably built against OpenGL ES, but I don't know if that matters when using PyOpenGL calls.
                FWIW, I don't see any errors when running your example on Linux with an otherwise very similar set up. Did you contribute to that PyQt mailing list thread yourself? I would have thought that was the place to go to get answers on issues like this.
– ekhumoro
                Dec 10, 2014 at 20:49
                It worked fine on Linux for me too. This problem is only reproducible on Windows, already tested on two machines. Perhaps I should indeed try the mailing list.
– kamokr
                Dec 10, 2014 at 23:08
You should use QtOpenGL.QGLWidget. The Qt.QWindow is not using OpenGL.
Here is a working example:
import struct
from PyQt5 import QtOpenGL, QtWidgets
import ModernGL
class QGLControllerWidget(QtOpenGL.QGLWidget):
    def __init__(self):
        fmt = QtOpenGL.QGLFormat()
        fmt.setVersion(3, 3)
        fmt.setProfile(QtOpenGL.QGLFormat.CoreProfile)
        fmt.setSampleBuffers(True)
        super(QGLControllerWidget, self).__init__(fmt, None)
    def initializeGL(self):
        self.ctx = ModernGL.create_context()
        prog = self.ctx.program([
            self.ctx.vertex_shader('''
                #version 330
                in vec2 vert;
                void main() {
                    gl_Position = vec4(vert, 0.0, 1.0);
            '''),
            self.ctx.fragment_shader('''
                #version 330
                out vec4 color;
                void main() {
                    color = vec4(0.30, 0.50, 1.00, 1.0);
            '''),
        vbo = self.ctx.buffer(struct.pack('6f', 0.0, 0.8, -0.6, -0.8, 0.6, -0.8))
        self.vao = self.ctx.simple_vertex_array(prog, vbo, ['vert'])
    def paintGL(self):
        self.ctx.viewport = (0, 0, self.width(), self.height())
        self.ctx.clear(0.9, 0.9, 0.9)
        self.vao.render()
        self.ctx.finish()
app = QtWidgets.QApplication([])
window = QGLControllerWidget()
window.move(QtWidgets.QDesktopWidget().rect().center() - window.rect().center())
window.show()
app.exec_()
I can only offer a workaround.
I can reproduce the problem on windows too. the glClearColor call is not the problem. The error occurs in context.create() or self.create() but pyOpenGL only notices it when it checks for errors after the first call. 
I don't know what actually causes the problem, but if I just ignore the error it works just fine. At the end of __init__ I add:
    self.context.makeCurrent(self)
    GL.glGetError()  # Ignore openGL error if one occured
        
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