'Update the size of the chunk'

def _update_size(self, data_size):

    self.__fileobj.seek((self.offset + 4))
    self.__fileobj.write(pack('>I', data_size))
    if (self.parent_chunk is not None):
        size_diff = (self.data_size - data_size)
        self.parent_chunk._update_size((self.parent_chunk.data_size - size_diff))
    self.data_size = data_size
    self.size = (data_size + self.HEADER_SIZE)
