title: process large text file in python
body: <p>I have a very large file (3.8G) that is an extract of users from a system at my school.  I need to reprocess that file so that it just contains their ID and email address, comma separated.</p>
  
  <p>I have very little experience with this and would like to use it as a learning exercise for Python.</p>
  
  <p>The file has entries that look like this:</p>
  
  <pre><code>dn: uid=123456789012345,ou=Students,o=system.edu,o=system
  LoginId: 0099886
  mail: fflintstone@system.edu
  
  dn: uid=543210987654321,ou=Students,o=system.edu,o=system
  LoginId: 0083156
  mail: brubble@system.edu
  </code></pre>
  
  <p>I am trying to get a file that looks like:</p>
  
  <pre><code>0099886,fflintstone@system.edu
  0083156,brubble@system.edu
  </code></pre>
  
  <p>Any tips or code?</p>