Exercise 1 solution

    import struct

    for fmt in ("hi", "bhb", "bbh", "qb", "bq"):
        print(fmt, struct.calcsize("@" + fmt), struct.calcsize("<" + fmt))
    print(struct.pack("@bi", 1, 2).hex(" "))
    print(struct.pack("<bi", 1, 2).hex(" "))
    print(struct.calcsize("@bxxxi"))

    # hi 8 6
    # bhb 5 4
    # bbh 4 4
    # qb 9 9
    # bq 16 9
    # 01 00 00 00 02 00 00 00
    # 01 02 00 00 00
    # 8

(Run as written; the output matched the comments. The native sizes are from
one machine and depend on its alignment rules (check on yours).)

Explanation: with the "@" prefix, each field starts at an offset that is a
multiple of its own size, so padding bytes are inserted. In "@hi" two padding
bytes sit after the 2-byte field so the 4-byte field starts at offset 4: size
8, against 6 with "<". In "@bhb" one padding byte goes after the first byte,
giving 5 (the trailing byte needs none). In "@bbh" the two single bytes fill
offsets 0 and 1 so the 2-byte field is already aligned and nothing is added.
In "@qb" the 8-byte field comes first, so there is nothing to pad before the
byte and no padding at the end. In "@bq" seven padding bytes are needed, so the
size is 16. Writing "@bxxxi" by hand gives the same 8 bytes as "@bi", which
shows the padding is just invisible "x" fields. With "<" there is never any
padding, so the size is the plain sum of the field sizes. Files should use a
"<" or ">" prefix so the layout does not depend on the machine.