title: how to create a list of lists
body: <p>My Python code generates a list everytime it loops:</p>
  
  <pre><code>list = np.genfromtxt('temp.txt', usecols=3, dtype=[('floatname','float')], skip_header=1)
  </code></pre>
  
  <p>But I want to save each one - I need a list of lists right?</p>
  
  <p>So I tried:</p>
  
  <pre><code>list[i] = np.genfromtxt('temp.txt', usecols=3, dtype=[('floatname','float')], skip_header=1)
  </code></pre>
  
  <p>But Python now tells me that "list" is not defined. I'm not sure how I go about defining it. Also, is a list of lists the same as an array??</p>
  
  <p>Thank you!</p>