title: Create file but if name exists add number
body: <p>Does Python have any built-in functionality to add a number to a filename if it already exists?</p>
  
  <p>My idea is that it would work the way certain OS's work - if a file is output to a directory where a file of that name already exists, it would append a number or increment it.</p>
  
  <p>I.e: if "file.pdf" exists it will create "file2.pdf", and next time "file3.pdf".</p>