title: zip() alternative for iterating through two iterables
body: <p>I have two large (~100 GB) text files that must be iterated through simultaneously.</p>
  
  <p>Zip works well for smaller files but I found out that it's actually making a list of lines from my two files.  This means that every line gets stored in memory.  I don't need to do anything with the lines more than once.</p>
  
  <pre><code>handle1 = open('filea', 'r'); handle2 = open('fileb', 'r')
  
  for i, j in zip(handle1, handle2):
      do something with i and j.
      write to an output file.
      no need to do anything with i and j after this.
  </code></pre>
  
  <p>Is there an alternative to zip() that acts as a generator that will allow me to iterate through these two files without using >200GB of ram?</p>