title: In python one list converted to dict like a tree topology
body: <p>In python2.7, I have one list </p>
  
  <pre><code>['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q']
  </code></pre>
  
  <p>and I need to transform into a dict like</p>
  
  <pre><code>{
  'A':['B','C'],
  'B':['D','E'],
  'C':['F','G'],
  'D':['H','I'],
  'E':['J','K'],
  'F':['L','M'],
  'G':['N','O'],
  'H':['P','Q'],
  'I':[],
  'J':[],
  'K':[],
  'L':[],
  'M':[],
  'N':[],
  'O':[],
  'P':[],
  'Q':[]
  }
  </code></pre>