title: How to merge dict keys with sum of values?
body: <p>I have 3 dicts</p>
  <pre><code>d1 = {&quot;a&quot;:[1], &quot;b&quot;:[2]}
  d2 = {&quot;b&quot;:[3], &quot;d&quot;:[1]}
  d3 = {&quot;a&quot;:[4], &quot;d&quot;:[2], &quot;c&quot;:[3]}
  </code></pre>
  <p>How can we merge dict so that key can remain same and value will be sum of lists?</p>
  <p>output</p>
  <pre><code>output = {&quot;a&quot;:5, &quot;b&quot;:5, &quot;c&quot;:3, &quot;d&quot;:3}
  </code></pre>