title: Difference between modes a, a+, w, w+, and r+ in built-in open function?
body: <p>In the python built-in <a href="http://docs.python.org/library/functions.html#open" rel="noreferrer">open</a> function, what is the exact difference between the modes <code>w</code>, <code>a</code>, <code>w+</code>, <code>a+</code>, and <code>r+</code>?</p>
  
  <p>In particular, the documentation implies that all of these will allow writing to the file, and says that it opens the files for "appending", "writing", and "updating" specifically, but does not define what these terms mean.</p>