book open('treasure txt'' 'file object starts with offset at start lines_a list(bookprint(lines_aoperation reads entire file from offset offset changed to end of file lines_b list(bookprint(lines_b[operation reads entire file from offset so there' nothing left to read recall that the reading starts at the offset and reads forwards -to the end of the file in this example it also moves the offset to what was last read so the offset is changed to refer to the end of the file