struct 0.1.0 on Edge Python

struct

struct works like Python’s. pack turns values into bytes by a format, unpack turns them back into a tuple, and calcsize says how many bytes a format takes.

import struct

data = struct.pack("<hif", 1, -2, 0.5)
print(data)
print(struct.unpack("<hif", data))
print(struct.calcsize("<hif"))

{
  "imports": {
    "struct": "https://cdn.edgepython.com/pkg/struct/0.1.0/app.edge#sha256-a9df20e63bf8ed4920a326dacd5bfa3ddf10a5948cb733a8d0377d3947bf12b7"
  }
}

b'\x01\x00\xfe\xff\xff\xff\x00\x00\x00?'
(1, -2, 0.5)
10

Output

A format starts with its byte order. < and > pick little and big endian with standard sizes, and a format with no prefix lays its items out the way C does, each aligned to its size.

import struct

print(struct.pack(">H", 258), struct.pack("<H", 258))
print(struct.calcsize("bi"), struct.calcsize("<bi"))

{
  "imports": {
    "struct": "https://cdn.edgepython.com/pkg/struct/0.1.0/app.edge#sha256-a9df20e63bf8ed4920a326dacd5bfa3ddf10a5948cb733a8d0377d3947bf12b7"
  }
}

b'\x01\x02' b'\x02\x01'
8 5

Output

s is a run of bytes padded or cut to its count, c one byte and ? a bool. A Struct keeps a format, unpack_from reads at an offset and iter_unpack walks a buffer of records.

import struct

record = struct.Struct("<4sH?")
data = record.pack(b"edge", 7, True) + record.pack(b"py", 8, False)
print(record.size, record.unpack_from(data, record.size))
for name, n, ok in record.iter_unpack(data):
    print(name, n, ok)

{
  "imports": {
    "struct": "https://cdn.edgepython.com/pkg/struct/0.1.0/app.edge#sha256-a9df20e63bf8ed4920a326dacd5bfa3ddf10a5948cb733a8d0377d3947bf12b7"
  }
}

7 (b'py\x00\x00', 8, False)
b'edge' 7 True
b'py\x00\x00' 8 False

Output

A value out of range or of the wrong kind raises struct.error, which is ValueError here, and a float too large for its code raises OverflowError. pack_into is not supported, since there is no writable buffer to pack into.

import struct

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

try:
    struct.pack("<e", 70000.0)
except OverflowError as e:
    print("too large:", e)

{
  "imports": {
    "struct": "https://cdn.edgepython.com/pkg/struct/0.1.0/app.edge#sha256-a9df20e63bf8ed4920a326dacd5bfa3ddf10a5948cb733a8d0377d3947bf12b7"
  }
}

out of range: 'B' format requires 0 <= number <= 255
too large: float too large to pack with e format

Output

struct

struct

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