title: Why doesn't cv.waitKey(0) pause execution until key is pressed?
body: <p>I had thought <code>cv.waitKey</code> would pause execution until a key was pressed, but it doesn't seem to be doing so. When I run the following code:</p>
  <pre><code>import cv2 as cv
  
  print(&quot;Start&quot;)
  k = cv.waitKey(0)
  print(&quot;Stop&quot;)
  </code></pre>
  <p>It does not wait for a key to be pressed before completing execution. Must there actually be an image shown for the delay to occur? Is there something (one of the many things) about event loop creation occurring, that I don't understand?</p>
  <p>(Note: I'm not just looking for something to act as an 'input' line. I'm currently using OpenCV with an eyetracker and was trying to figure out why OpenCV seems to block the callback function of the eyetracker, when I ran into this misunderstanding.)</p>