title: Python or Python3. What is the difference?
body: <p>What is the difference between following commands:</p>
  <pre><code>python setup.py
  </code></pre>
  <p>and</p>
  <pre><code>python3 setup.py
  </code></pre>
  <ul>
  <li>What if I only have python3.6 installed? <code>python</code> and <code>python3</code> would do the same thing?</li>
  <li>Does it make difference only when I have different versions of python installed? If so, which version will be used with <code>python setup.py</code>?</li>
  </ul>