title: how to loop from 0000 to 9999 and convert the number to the relative string?
body: <p>i want to get some string, range from 0000 to 9999, that's to say, i want to print the following string:</p>
  
  <pre><code>0000
  0001
  0002
  0003
  0004
  0005
  0006
  ....
  9999
  </code></pre>
  
  <p>i tried to use <code>print "\n".join([str(num) for num in range(0, 9999)])</code>, but failed, i get the following number:</p>
  
  <pre><code>0
  1
  2
  3
  4
  5
  6
  ...
  9999
  </code></pre>
  
  <p>i want python to add the prefix <strong><em>0</em></strong> automatically, making the number remain <strong><em>4 bit digits</em></strong> all the time. can anyone give a hand to me? any help appreciated.</p>