Python module introduction-struct binary data structure

Python module introduction-conversion of binary and string data in struct binary data structure
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# Reference: The PythonStandard Libraryby Example 2011

Converts byte data and python data types. The format indicator has the same mutations mechanism as the re module. Therefore, creating a Struct instance and calling an instance method is more effective than using a module function.

Package and package:

File: struct_pack.py

Import binascii

 

Values = (1, 'AB', 2.7)

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

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)

Execution result:

Original values: (1, 'AB', 2.7)

Format string: I 2 s f

Uses: 12 bytes

Packed Value: 000000061620000cdcc2c40

 

File: struct_unpack.py

Import struct

Import binascii

 

Packed_data = binascii. unhexlify ('000000061620000cdcc2c40 ')

 

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

Unpacked_data = s. unpack (packed_data)

Print 'unpacked Values: ', unpacked_data

Execution result:

Unpacked Values: (1, 'AB', 2.700000047683716)

Byte order:

Import struct

Import binascii

 

Values = (1, 'AB', 2.7)

Print 'original values: ', values

 

Endianness = [

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

('=', 'Native, standard '),

('<', 'Little-endian '),

('>', 'Big-endian '),

('! ', 'Network '),

]

 

For code, name in endianness:

S = struct. Struct (code + 'i2s 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)

Execution result:

Original values: (1, 'AB', 2.7)

Format string: @ I 2 s f fornative, native

Uses: 12 bytes

Packed Value: 000000061620000cdcc2c40

Unpacked Value: (1, 'AB', 2.700000047683716)

 

Format string: = I 2 s f fornative, standard

Uses: 10 bytes

Packed Value: 010000006162cdcc2c40

Unpacked Value: (1, 'AB', 2.700000047683716)

 

Format string: <I 2 s f forlittle-endian

Uses: 10 bytes

Packed Value: 010000006162cdcc2c40

Unpacked Value: (1, 'AB', 2.700000047683716)

 

Format string:> I 2 s f forbig-endian

Uses: 10 bytes

Packed Value: 000000016162402 ccccd

Unpacked Value: (1, 'AB', 2.700000047683716)

 

Format string :! I 2 s f fornetwork

Uses: 10 bytes

Packed Value: 000000016162402 ccccd

Unpacked Value: (1, 'AB', 2.700000047683716)

When performance requirements are high, you can use buffer. pack_into () and unpack_from () can directly interact with buffer.

Import struct

Import binascii

 

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

Values = (1, 'AB', 2.7)

Print 'original: ', values

 

Print

Print 'ctypes string buffer'

 

Import ctypes

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'

 

Import array

A = array. array ('C', '\ 0' * s. size)

Print 'before: ', binascii. hexlify ()

S. pack_into (a, 0, * values)

Print 'after: ', binascii. hexlify ()

Print 'unpacked: ', s. unpack_from (a, 0)

Execution result:

Original: (1, 'AB', 2.7)

 

Ctypes string buffer

Before: 000000000000000000000000

After: 0100000061620000cdcc2c40

Unpacked: (1, 'AB', 2.700000047683716)

 

Array

Before: 000000000000000000000000

After: 0100000061620000cdcc2c40

Unpacked: (1, 'AB', 2.700000047683716)

 

The Struct module can work with namedtuple to make binary data more readable:

>>> Record = 'raymond \ x32 \ x12 \ x08 \ x01 \ x08'

>>> Name, serialnum, school, gradelevel = unpack ('<10sHHb', record)

 

>>> From collections import namedtuple

>>> Student = namedtuple ('student ', 'name serialnum schoolgradelevel ')

>>> Student. _ make (unpack ('<10sHHb', record ))

Student (name = 'raymond ', serialnum = 4658, school = 264, gradelevel = 8)

 

Similar modules: xdrlib, array