code: def encode(text):
      """Encode a unicode string as a list of tokens.
  
      Args:
        text: a unicode string
      Returns:
        a list of tokens as Unicode strings
      """
      if not text:
          return []
      ret = []
      token_start = 0
      # Classify each character in the input string
      is_alnum = [c in _ALPHANUMERIC_CHAR_SET for c in text]
      for pos in range(1, len(text)):
          if is_alnum[pos] != is_alnum[pos - 1]:
              token = text[token_start:pos]
              if token != " " or token_start == 0:
                  ret.append(token)
              token_start = pos
      final_token = text[token_start:]
      ret.append(final_token)
      return ret
  
file_path: trax/trax/data/tokenizer.py
imports: import collections
  import sys
  import unicodedata
  from absl import logging
  import six
  import tensorflow
label_desc: Use image node_id 1 for calling a global function with example usage: encode(text) and returns: ret, list