title: python yaml.dump format list in other YAML format
body: <p>I want to dump a Python object to a YAML file like this:</p>
  
  <pre><code>a: 5
  b: 6
  c: 7
  d: [ 1,2,3,4]
  </code></pre>
  
  <p>but NOT</p>
  
  <pre><code>a: 5 
  b: 6
  c: 7
  d 
  - 1
  - 2
  - 3
  - 4
  </code></pre>
  
  <p>image d was a massive list, the output gets messy for humans to see.</p>
  
  <p>I use: <code>default_flow_style=False</code> but this uses the new line list item format.</p>
  
  <p>I already use a customer dumper to stop anchors.</p>