code: def clean_single_word(word, lemmatizing="wordnet"):
      
      if lemmatizing == "porter":
          porter = PorterStemmer()
          lemma = porter.stem(word)
      elif lemmatizing == "snowball":
          snowball = SnowballStemmer('english')
          lemma = snowball.stem(word)
      elif lemmatizing == "wordnet":
          wordnet = WordNetLemmatizer()
          lemma = wordnet.lemmatize(word)
      else:
          print("Invalid lemmatizer argument.")
          raise RuntimeError
  
      return lemma
docs: Performs stemming or lemmatizing on a single word.
  
      If we are to search for a word in a clean bag-of-words, we need to search it after the same kind of preprocessing.
  
      Inputs: - word: A string containing the source word.
              - lemmatizing: A string containing one of the following: "porter", "snowball" or "wordnet".
  
      Output: - lemma: The resulting clean lemma or stem.