code: def ensure_str(s, encoding="utf-8", errors="strict"):
      
      if six.PY3:
          text_type = str
          binary_type = bytes
      else:
          text_type = unicode  # noqa: F821
          binary_type = str
      if not isinstance(s, (text_type, binary_type)):
          raise TypeError("not expecting type '%s'" % type(s))
      if six.PY2 and isinstance(s, text_type):
          s = s.encode(encoding, errors)
      elif six.PY3 and isinstance(s, binary_type):
          s = s.decode(encoding, errors)
      return s
docs: Coerce *s* to `str`.
  
      To keep six with lower version, see Issue 4169, we copy this function
      from six == 1.12.0.
  
      TODO(yuhguo): remove this function when six >= 1.12.0.
  
      For Python 2:
        - `unicode` -> encoded to `str`
        - `str` -> `str`
  
      For Python 3:
        - `str` -> `str`
        - `bytes` -> decoded to `str`