title: What does an exclamation mark (!) before a statement do?
body: <p>I was trying to install the dark theme in Jupyter notebook by typing this in notebook</p>
  
  <pre><code>pip install jupyterthemes
  jt -t chesterish
  </code></pre>
  
  <p>The first command worked but I got some error in the 2nd one. Then I wrote this</p>
  
  <pre><code>!jt -t chesterish
  </code></pre>
  
  <p>And it worked. What did the exclamation mark do?</p>
  
  <p>P.S. I am extremely new to python, just started last week</p>