title: how to sum two numbers in a list?
body: <p><strong>what is the solution of this by  python 3 ?</strong> </p>
  
  <blockquote>
    <p>Given an array of integers, return indices of the two numbers such that they add up to a specific target.
    You may assume that each input would have exactly one solution, and you may not use the same element twice.</p>
  </blockquote>
  
  <p>Example:</p>
  
  <pre><code>Given nums = [2, 7, 11, 15], target = 9,
  Because nums[0] + nums[1] = 2 + 7 = 9,
  return [0, 1]. 
  </code></pre>