title: python one line save values of lists in dict to list
body: <p>I would like to write for loop in one line:</p>
  
  <pre><code>d = {'a': [1, 2, 3], 'b': [5, 6, 7], 'c': [9, 0]}
  
  my_list = []
  for k, v in d.items():
      for x in v:
          my_list.append(x)
  </code></pre>
  
  <p>How can I do it?</p>