title: this code works on windows but giving error on Linux "QApplication was not created in main thread" ,how to resolve it,
body: <pre><code>import cv2
  import threading
  
  class camThread(threading.Thread):
      def __init__(self, previewName, camID):
  
          threading.Thread.__init__(self)
          self.previewName = previewName
          self.camID = camID
  
      def run(self):
  
          print "Starting " + self.previewName
          camPreview(self.previewName, self.camID)
  
  def camPreview(previewName, camID):
      cv2.namedWindow(previewName)
      cam = cv2.VideoCapture(camID)
      if cam.isOpened():  # try to get the first frame
  
          rval, frame = cam.read()
  
      else:
  
          rval = False
      while rval:
  
          cv2.imshow(previewName, frame)
          rval, frame = cam.read()
          key = cv2.waitKey(20)
          if key == 27:  
  
              break
      cv2.destroyWindow(previewName)
  
  # Create two threads as follows
  
  thread1 = camThread("Camera 1", 1)
  thread2 = camThread("Camera 2", 2)
  
  thread1.start()
  thread2.start()
  </code></pre>