title: What's the difference between opening a file for update and just appending?
body: <p>As in, when opening a file with <code>open()</code>, why do we have modes 'r+', 'w+', 'a+'? Surely mode 'a' does the same job? I'm especially confused by the difference between modes 'a' and 'a+' - could someone explain where they differ and, if possible, when one should use one or the other?</p>