title: Search for specific string, only copy part of string into another textfile
body: <p>I want my python program to search a text file for a specific portion of a string.
  For example, my text file looks like this:</p>
  
  <pre><code>VERSION_1_0001
  VERSION_2_0012
  VERSION_3_0391
  </code></pre>
  
  <p>These are just examples. I want my python program to look for "VERSION_2_" but have it print out 0012 in another text file. Is that possible?</p>
  
  <p>So far I just have this:</p>
  
  <pre><code>with open('versions.txt', 'r') as verFile:
      for line in verFile:
          if 'VERSION_2_' in line:
              ??? (I don't know what would go here so I can get the portion attached to the string I'm finding)
  </code></pre>
  
  <p>Thanks for the help in advance!</p>