title: How to iterate over all values of an Enum including any nested Enums?
body: <p>Imagine one has two classes derived from <code>Enum</code>, e.g.</p>
  
  <pre><code>class Color(Enum):
      blue = 'blue'
      red = 'red'
  
  class Properties(Enum):
      height = 'h'
      weight = 'w'
      colors = Color
  
  </code></pre>
  
  <p>What is the best way to (probably recursively) iterate over all Enum-labels of a nested Enum like <code>Properties</code>, including the ones of <code>Enum</code>-members like <code>Properties.colors</code> in the example above (i.e. including  <code>Color.blue</code> and <code>Color.red</code>)? Checking for the type of the value?</p>