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 != u" " or token_start == 0:
        ret.append(token)
      token_start = pos
  final_token = text[token_start:]
  ret.append(final_token)
  return ret
Encode a unicode string as a list of tokens.

  Args:
    text: a unicode string
  Returns:
    a list of tokens as Unicode strings
  
trax/data/tokenizer.py