title: Create file of single instances of account number
body: <p>I have a list of account numbers, separated by line, generated by a log of transactions.</p>
  
  <p>How do I consolidate this list into a file that will have only one occurrence of each account instead of many (where more than one transaction per account has been logged)?</p>
  
  <p>Python is preferred but I can also use C.</p>