title: os.path.join in python returns 'wrong' path?
body: <p>I have the following python os.path output from ipython</p>
  
  <pre><code>import os.path as path
  path.join("/", "tmp")
  Out[4]: '/tmp'
  path.join("/", "/tmp")
  Out[5]: '/tmp'
  path.join("abc/", "/tmp")
  Out[6]: '/tmp'
  path.join("abc", "/tmp")
  Out[7]: '/tmp'
  path.join("/abc", "/tmp")
  Out[8]: '/tmp'
  path.join("def", "tmp")
  Out[10]: 'def/tmp'
  </code></pre>
  
  <p>I find outputs 5, 6, 7 and 8 to be counterintuitive. Can somebody please explain if there was a specific reason for this implementation? </p>