parameters: (feature)
docstring: Generates an error if the feature is unknown.
docstring_summary: Generates an error if the feature is unknown.
docstring_tokens: Generates an error if the feature is unknown .
function: def __validate_feature (feature):
      """ Generates an error if the feature is unknown.
      """
      assert isinstance(feature, basestring)
      if feature not in __all_features:
          raise BaseException ('unknown feature "%s"' % feature)
function_tokens: def __validate_feature ( feature ) : assert isinstance ( feature , basestring ) if feature not in __all_features : raise BaseException ( 'unknown feature "%s"' % feature )