title: Python creating nested dictionary from a List with repeating keys
body: <p>I am trying to convert the list to a dictionary. 
  I have a list of list like this and some of the first values of mini lists are repeating:</p>
  
  <pre><code>list = [["DDS 500","A",300], ["DDS 500","B",100], ["AGB 850","C",250], ["AGB 850","B",350], ["UNI 100","D",900]]
  </code></pre>
  
  <p>The first value of mini lists will be key . Then, for each mini list second and third value  will be the "value" for that key and the values also should be a dictionary. As a result, Final dictionary should be like this:</p>
  
  <pre><code>dict = { "DDS 500":{"A":300,"B":100}, "AGB 850":{"C":250,"B":350}, "UNI 100":{"D":900} }
  
  </code></pre>