code: def could_be_unfinished_char(seq, encoding):
      
      if decodable(seq, encoding):
          return False # any sensible encoding surely doesn't require lookahead (right?)
          # (if seq bytes encoding a character, adding another byte shouldn't also encode something)
  
      if encodings.codecs.getdecoder('utf8') is encodings.codecs.getdecoder(encoding):
          return could_be_unfinished_utf8(seq)
      elif encodings.codecs.getdecoder('ascii') is encodings.codecs.getdecoder(encoding):
          return False
      else:
          return True
docs: Whether seq bytes might create a char in encoding if more bytes were added