code: def check_ascii_256(string):
      
      if string is None:
          return
      if len(string) > 256:
          raise ValueError("Value is longer than 256 characters")
      bad_char = _NON_PRINTABLE_ASCII.search(string)
      if bad_char:
          raise ValueError(u'Character "{}" at position {} is not printable '
                           'ASCII'
                           .format(
                               string[bad_char.start():bad_char.end()],
                               bad_char.start()))
docs: Check that `string` is printable ASCII and at most 256 chars.
  
      Raise a `ValueError` if this check fails. Note that `string` itself doesn't
      have to be ASCII-encoded.
  
      :type string: str
      :param string: The string to check.