python struct binascii

struct_pack.py

# https://pymotw.com/3/struct/
# struct_pack.py
import struct
import binascii

values = (1, 'ab'.encode('utf-8'), 2.7)
s = struct.Struct('I 2s f')
packed_data = s.pack(*values)

print('Original values:', values)
# (1, b'ab', 2.7)
print('Format string  :', s.format)
# b'I 2s f'
print('Uses           :', s.size, 'bytes')
# 12 bytes
print('Packed Value   :', binascii.hexlify(packed_data))
# b'0100000061620000cdcc2c40'


# struct_unpack.py
import struct
import binascii

packed_data = binascii.unhexlify(b'0100000061620000cdcc2c40')
s = struct.Struct('I 2s f')
unpacked_data = s.unpack(packed_data)
print('Unpacked Values:', unpacked_data)
# (1, b'ab', 2.700000047683716)


# struct_endianness.py
import struct
import binascii

values = (1, 'ab'.encode('utf-8'), 2.7)
print('Original values:', values)

endianness = [
  ('@', 'native, native'),
  ('=', 'native, standard'),
  ('<', 'little-endian'),
  ('>', 'big-engian'),
  ('!', 'network'),
]

for code, name in endianness:
  s = struct.Struct(code + ' I 2s f')
  packed_data = s.pack(*values)
  print()
  print('Format string  :', s.format, 'for', name)
  print('Uses           :', s.size, 'bytes')
  print('Packed Value   :', binascii.hexlify(packed_data))
  print('Unpacked Value :', s.unpack(packed_data))
  
# Byte Order Specifiers for struct
# Code Meaning
# @    Native order
# =    Native standard
# <    little-endian
# >    big-endian
# !    Network order


# struct_buffers.py
import array
import binascii
import ctypes
import struct

s = struct.Struct('I 2s f')
values = (1, 'ab'.encode('utf-8'), 2.7)
print('Original:', values)

print()
print('ctypes string buffer')

b = ctypes.create_string_buffer(s.size)
print('Before  :', binascii.hexlify(b.raw))
s.pack_into(b, 0, *values)
print('After   :', binascii.hexlify(b.raw))
print('Unpacked:', s.unpack_from(b, 0))

print()
print('array')

a = array.array('b', b'\0' * s.size)
print('Before :', binascii.hexlify(a))
s.pack_into(a, 0, *values)
print('After  :', binascii.hexlify(a))
print('Unpacked:', s.unpack_from(a, 0))