class_docstr: Process unit for token stemming.
  
  :param stemmer: stemmer to use, `porter` or `lancaster`.
class_docstr_tok: ["Process","unit","for","token","stemming",".",":","param","stemmer",":","stemmer","to","use",",","`","porter","`","or","`","lancaster","`","."]
docstr: Reducing inflected words to their word stem, base or root form.
  
  :param input_: list of string to be stemmed.
docstr_tok: ["Reducing","inflected","words","to","their","word","stem",",","base","or","root","form",".",":","param","input_",":","list","of","string","to","be","stemmed","."]
code: def transform(self, input_: list) -> list:
      """
      Reducing inflected words to their word stem, base or root form.
  
      :param input_: list of string to be stemmed.
      """
      if self.stemmer == "porter":
          porter_stemmer = nltk.stem.PorterStemmer()
          return [porter_stemmer.stem(token) for token in input_]
      elif self.stemmer == "lancaster" or self.stemmer == "krovetz":
          lancaster_stemmer = nltk.stem.lancaster.LancasterStemmer()
          return [lancaster_stemmer.stem(token) for token in input_]
      else:
          raise ValueError(
              "Not supported supported stemmer type: {}".format(
                  self.stemmer
              )
          )
  
imports: import nltk
  from .unit import Unit
label_desc: Use image node_id 2 for calling the Stemming obj's underlying member method code with example usage: obj.transform(input_) and returns: unknown, unknown