title: What is the return value of os.system() in Python?
body: <p>I came across this:</p>
  
  <pre><code>&gt;&gt;&gt; import os
  &gt;&gt;&gt; os.system('ls')
  file.txt README
  0
  </code></pre>
  
  <p>What is return value of <a href="https://docs.python.org/2/library/os.html#os.system"><code>os.system()</code></a>?  Why I get 0?</p>