title: Python os.path.relpath behavior
body: <p>I have a directory <code>bar</code> inside a directory <code>foo</code>, with file <code>foo_file.txt</code> in directory <code>foo</code> and file <code>bar_file.txt</code> in directory <code>bar</code>; i.e.</p>
  
  <pre><code>computer$ ls
  foo/
  computer$ ls foo/
  bar/  foo_file.txt
  computer$ ls foo/bar/
  bar_file.txt
  </code></pre>
  
  <p>Using the python <a href="http://docs.python.org/2/library/os.path.html#os.path.relpath" rel="noreferrer">os.path.relpath</a> function, I expect:</p>
  
  <pre><code>os.path.relpath('foo/bar/bar_file.txt', 'foo/foo_file.txt')
  </code></pre>
  
  <p>to give me:</p>
  
  <pre><code>'bar/bar_file.txt'
  </code></pre>
  
  <p>However, it actually gives me:</p>
  
  <pre><code>'../bar/bar_file.txt'
  </code></pre>
  
  <p>Why is this?  Is there an easy way to get the behavior I want?</p>
  
  <p>EDIT: This is on Linux with Python 2.7.3</p>