title: Creating dictionary from nested list using dictionary comprehension
body: <p>Is there a way to create a dictionary with a nested list but for specific indices?<br>
  I have input:</p>
  
  <pre><code> data = [[int, int, int], [int, int, int], [int, int,int]]
  </code></pre>
  
  <p>I want to so something along the lines of: </p>
  
  <pre><code>my_dictionary = {}
      for x in data:
         my_dictionary[x[0]] = []
         my_dictionary[x[1]] = []
  </code></pre>
  
  <p>but without having to iterate through the whole thing.</p>
  
  <p>For example:</p>
  
  <pre><code>data = [[a,b,c], [d,e,f], [g,h,i]] 
  # would leave me with:
  my_dictionary = {a: [] , b:[], d:[], e:[], g:[], h:[] }
  </code></pre>
  
  <p>Is there a way to specify this using dictionary comprehension?</p>