code: def of(cls, value):
          
          if isinstance(value, ConfigSource):
              return value
          elif isinstance(value, dict):
              return ConfigSource(value)
          else:
              raise TypeError(u'source value must be a dict')
docs: Given either a dictionary or a `ConfigSource` object, return
          a `ConfigSource` object. This lets a function accept either type
          of object as an argument.