title: Undo a file readline() operation so file-pointer is back in original state
body: <p>I'm browsing through a Python file pointer of a text file in read-only mode using file.readline() looking for a special line.  Once I find that line I want to pass the file pointer to a method that is expecting the file pointer to be at the START of that readline (not right after it.)</p>
  
  <p>How do I essentially undo one file.readline() operation on a file pointer?</p>