title: List duplicates manipulation
body: <p>I am very new to python, and I am really lost right now. If anyone can help me, I will appreciate it a lot.
  I have a list:</p>
  <pre><code>list1 = [((a, b), 2), ((a, b), 5), ((c, d), 1)), ((e, f), 2), ((e, f), 4)]
  </code></pre>
  <p>The output I am looking for is:</p>
  <pre><code>output = [((a, b), 7), ((c, d), 1), ((e, f), 6)]
  </code></pre>
  <p>I tried to put it in a dictionary</p>
  <pre><code>new_dict = {i: j for i, j in list1}
  </code></pre>
  <p>But it throws me an error</p>
  <p>Maybe there are other ways?</p>