title: Python script header
body: <p>The typical header should be </p>
  
  <pre><code>#!/usr/bin/env python
  </code></pre>
  
  <p>But I found below also works when executing the script like <code>$python ./my_script.py</code></p>
  
  <pre><code>#!/usr/bin/python
  #!python
  </code></pre>
  
  <p>What's difference between these 2 headers? What could be the problem for 2nd one? Please also discussing the case for python interpreter is in PATH or not. Thanks.</p>