code: def tokenize(self, s):
      
      s = tf.compat.as_text(s)
  
      if self.reserved_tokens:
        # First split out the reserved tokens
        substrs = self._reserved_tokens_re.split(s)
      else:
        substrs = [s]
  
      toks = []
      for substr in substrs:
        if substr in self.reserved_tokens:
          toks.append(substr)
        else:
          toks.extend(self._alphanum_re.split(substr))
  
      # Filter out empty strings
      toks = [t for t in toks if t]
      return toks
docs: Splits a string into tokens.