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## struct

# struct is used to convert between binary and string types

# there are functions for doing struct things, but generally it's more efficient

# to make a Struct object and use its methods instead

import struct, binascii, ctypes, array

values = [1, 'ab', 2.7]

s = struct.Struct('I 2s f')

endianess = [

('@', 'native, native'),

('=', 'native, standard'),

('<', 'little-endian'),

('>', 'big-endian'),

('!', 'network'),

]

packed_data = s.pack(*values)

print 'Original values:', values

print 'Format String :', s.format

print 'Uses :', s.size, 'bytes'

print 'Packed Value :', binascii.hexlify(packed_data)

print 'Unpacked Value :', s.unpack(packed_data)

for code, name in endianess:

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 Values:', s.unpack(packed_data)

# Since most of the reasons to be working with binary packed data coincide with

# good reasons to optimize code, it's best to use the same buffer to minimise overhead

s = struct.Struct('I 2s f')

values = (1, 'ab', 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('c', '\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)