@classmethod
def get_singleton(cls, annotators=None, **options):
    """
        Get or create a corenlp parser with the given annotator and options
        Note: multiple parsers with the same annotator and different options
              are not supported.
        """
    if annotators is not None:
        annotators = tuple(annotators)
    if annotators not in cls._singletons:
        cls._singletons[annotators] = cls(annotators, **options)
    return cls._singletons[annotators]
