title: Summarize the second elements in list of tuples if first elements are the same?
body: <p>HOW could Summarize the second elements in list of tuples,
  if first elements are the same?</p>
  <p>for example :</p>
  <p>in this</p>
  <pre><code>lst = [('milk', '2.35'), ('bread', '1.95'), ('chips', '2.54'), 
         ('milk', '2.38'), ('milk', '2.31'), ('bread', '1.90')]
  </code></pre>
  <p>I would summarize second elements of milk together and
  summarize second elements of bread together.</p>
  <p>and return this list:</p>
  <pre><code>[('bread', '3.85'), ('chips', '2.54'), ('milk', '7.04')]
  
  def my_def(a):
      my_list = []
      for item in a:
          if item[0] not in my_list:
              my_list.append(item[0])
      return my_list
  </code></pre>
  <p>I could just find same one :(</p>