old_contents: # Time:  ctor:   O(n), n is number of words in the dictionary. 
  #        lookup: O(1)
  # Space: O(k), k is number of unique words.
  
  class ValidWordAbbr(object):
      def __init__(self, dictionary):
          """
          initialize your data structure here.
          :type dictionary: List[str]
          """
          self.lookup_ = collections.defaultdict(set)
          for word in dictionary:
              abbr = self.abbreviation(word)
              self.lookup_[abbr].add(word)
              
  
      def isUnique(self, word):
          """
          check if a word is unique.
          :type word: str
          :rtype: bool
          """
          l = len(word)
          abbr = self.abbreviation(word)
          return self.lookup_[abbr] <= {word}
  
  
      def abbreviation(self, word):
          return word[0] + str(len(word)) + word[-1]
  
  
  # Your ValidWordAbbr object will be instantiated and called as such:
  # vwa = ValidWordAbbr(dictionary)
  # vwa.isUnique("word")
  # vwa.isUnique("anotherWord")
  
new_contents: # Time:  ctor:   O(n), n is number of words in the dictionary. 
  #        lookup: O(1)
  # Space: O(k), k is number of unique words.
  
  class ValidWordAbbr(object):
      def __init__(self, dictionary):
          """
          initialize your data structure here.
          :type dictionary: List[str]
          """
          self.lookup_ = collections.defaultdict(set)
          for word in dictionary:
              abbr = self.abbreviation(word)
              self.lookup_[abbr].add(word)
              
  
      def isUnique(self, word):
          """
          check if a word is unique.
          :type word: str
          :rtype: bool
          """
          abbr = self.abbreviation(word)
          return self.lookup_[abbr] <= {word}
  
  
      def abbreviation(self, word):
          if len(word) <= 2:
              return word
          return word[0] + str(len(word)-2) + word[-1]
  
  
  # Your ValidWordAbbr object will be instantiated and called as such:
  # vwa = ValidWordAbbr(dictionary)
  # vwa.isUnique("word")
  # vwa.isUnique("anotherWord")
  
subject: fix minor error