struct (js, cli)

struct packs primitive values into bytes and back. Declare it with edge add struct and import it by bare name. To pin a different version, point the edge.json entry at another URL, see Modules.

Functions are pack(fmt, *values), unpack(fmt, data), and calcsize(fmt). Codes are x b B ? h H i I q Q f d with repeat counts, and byte-order prefixes are < (the default), =, >, !. There is no native-alignment mode. unpack returns a list. A packed buffer crosses the host boundary once, which makes it the fast lane for bulk numeric data. Out-of-range integers raise ValueError, non-integer values for integer codes raise TypeError, and f / d accept integers. Not implemented: s / p strings, e half floats, n / N, and pack_into / unpack_from / iter_unpack.

from struct import pack, unpack, calcsize

buf = pack("3f", 92.5, -115.25, 0.75)
print(unpack("3f", buf))
print(calcsize("!hh"))

cmd + enter

[92.5, -115.25, 0.75]
4

Output

The byte-order prefix picks the layout:

from struct import pack, unpack

print(pack("<H", 258))
print(pack(">H", 258))
print(unpack("!I", pack("!I", 70000)))

cmd + enter

b'\x02\x01'
b'\x01\x02'
[70000]

Output

A value that does not fit its code raises ValueError:

from struct import pack

try:
    pack("B", 300)
except ValueError as e:
    print("out of range:", e)

cmd + enter

out of range: argument out of range for 'B'

Output