title: How to test if an Enum member with a certain name exists?
body: <p>Using Python 3.4 I want to test whether an Enum class contains a member with a certain name.</p>
  
  <p>Example:</p>
  
  <pre><code>class Constants(Enum):
      One = 1
      Two = 2
      Three = 3
  
  print(Constants['One'])
  print(Constants['Four'])
  </code></pre>
  
  <p>gives:</p>
  
  <pre><code>Constants.One
    File "C:\Python34\lib\enum.py", line 258, in __getitem__
      return cls._member_map_[name]
  KeyError: 'Four'
  </code></pre>
  
  <p>I could catch the <code>KeyError</code> and take the exception as indication of existence but maybe there is a more elegant way?</p>