def chunklentype(self):
        """Reads just enough of the input to determine the next
        chunk's length and type, returned as a (*length*, *type*) pair
        where *type* is a string.  If there are no more chunks, ``None``
        is returned.
        """

        x = self.file.read(8)
        if not x:
            return None
        if len(x) != 8:
            raise FormatError(
              'End of file whilst reading chunk length and type.')
        length,type = struct.unpack('!I4s', x)
        if length > 2**31-1:
            raise FormatError((type,length) % 'Chunk %s is too large: %d.')
        return length,type
dataset/ETHPy150Open jyapayne/Web2Executable/png.py/Reader.chunklentype/swapped operands of `%`