class_docstr: Splits a string into tokens, and joins them back.
class_docstr_tok: ["Splits","a","string","into","tokens",",","and","joins","them","back","."]
code: def alphanum_only(self):
      return self._alphanum_only
  
imports: from __future__ import unicode_literals
  import abc
  import hashlib
  import json
  import re
  from tensorflow_datasets.core.utils.lazy_imports_utils import tensorflow
label_desc: Use image node_id 2 for calling the Tokenizer obj's underlying member method code with example usage: obj.alphanum_only() and returns: self