title: Python numpy scientific notation limit decimals
body: <p>I'm trying to reduce the number of decimals that I'm getting after some calculations. The <code>print()</code> where my problem arises looks like this:</p>
  
  <pre><code>print("Mean resistivity: {res} Ohm m".format(res=np.mean(resistivity)))
  </code></pre>
  
  <p>And it outputs this:</p>
  
  <pre><code>Mean resistivity: 1.6628449915450776e-08 Ohm m
  </code></pre>
  
  <p>Now I want to reduce the number of decimal places that are printed to 3. I tried doing it with string formatting, like this:</p>
  
  <pre><code>print("Mean resistivity: {res:.3f} Ohm m".format(res=np.mean(resistivity)))
  </code></pre>
  
  <p>However, this code prints:</p>
  
  <pre><code>Mean resistivity: 0.000 Ohm m
  </code></pre>
  
  <p>What I actually want is this:</p>
  
  <pre><code>Mean resistivity: 1.663e-8 Ohm m
  </code></pre>
  
  <p>How can I format <code>res</code> to only be displayed as scientific notation but with only 3 decimal places?</p>