title: File iteration, checking line existence
body: <p>I am reading through a file using a for loop like this...</p>
  
  <pre><code>f = open("somefile.txt")
  
  for line in f:
      do stuff
  </code></pre>
  
  <p>except for each line I read i need to take an item from the line ahead of it and put it in the current line. What is the best way to do this? Is there a way to read the next line or get some item from it without reading it?</p>