How to use return value of a function as condition of while that returns tuple in python -

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I was looking for something like this but I did not know that it goes here.

Some backgrounds

I use opencv to get the frame from a video file. Usually people do this in the endless loop: 

  while (true): s, img = cv.read ()   
 or  
  for i in xrange (10000): # large number, img = cv.read ()   
 Now I want to recover all frames and loop I want to leave when there is no other frame, though my skills in dragon is not enough which I want to do.  
  What I want to know   
  read  function (or method, I do not know how they are called in Python ) A tube gives: First represents the success of the operation, and the second frame returns the frame when I want to break the loop when the first element of tuple is false. Being a background, I thought it would work:  
  while ((success, img = capture. Read ()) [0]): # sdh with img   
 I thought it would break the loop when success would be false but it was not. Then I thought it would work:  
  while ((success, IMG = Capture.Red). Success: #Ads with IMG   
 It also did not work. I do not want to do anything like that (while): s, i = capture.read () if (s == wrong): break  < / Pre> 
 How can test the status of  in , a  if  breaks if it does not succeed?   < P> 
 
 best to think of dragon Do not forget other languages ​​ 
  s = true while s: s, i = capture.read () if S: do_some_stuff (i)

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