title: What's the effect of `pass` in Python debug mode
body: <p>I just found this phenomenon by coincidence. </p>
  
  <pre><code>mylist = [('1',), ('2',), ('3',), ('4',)]
  for l in mylist:
      print(l)
      pass    # first pass
  pass        # second pass
  print("end")
  </code></pre>
  
  <p>If I set the red stop point at the first <code>pass</code> and debug, the program will stop here and the output is:</p>
  
  <p><code>('1',)</code></p>
  
  <p>However, if I set the red stop point at the second <code>pass</code> and debug, the output include the <code>end</code> in the last line. It seems like the <code>pass</code> avoid stopping at this point and just let the program run further. </p>
  
  <p>I thought <code>pass</code> should have no real meaning, but it seems not. So how can understand the <code>pass</code>?</p>
  
  <p>Thank you all</p>