text: from nltk.tokenize import word_tokenize
  
  
  class Tokenizer(object):
      """ Interface. """
      def __init__(self, text):
          """ Constructor. """
          self.text = text
  
      def execute(self):
          """ Raises NotImplementedError. """
          raise NotImplementedError("Tokenizer is an abstract class. In must be "
                                    "implemented by another class. Try using "
                                    "the NLTKTokenizer.")
  
  
  class NLTKTokenizer(Tokenizer):
      """ Implements Tokenizer. """
      def __init__(self, text):
          """ Constructor. """
          super(NLTKTokenizer, self).__init__(text)
  
      def execute(self):
          """ Return a list of all tokens within the specified string. """
          return word_tokenize(self.text)
  