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This module performs conversions between Python values and C bit field structs represented as Python byte strings.

Project description

buildstatus

About

This module is intended to have a similar interface as the python struct module, but working on bits instead of primitive data types (char, int, …).

Documentation: http://bitstruct.readthedocs.org/en/latest

Installation

pip install bitstruct

Example usage

See the test suite: https://github.com/eerimoq/bitstruct/blob/master/tests/test_bitstruct.py

A basic example of packing/unpacking four integers:

>>> from bitstruct import *
>>> pack('u1u3u4s16', 1, 2, 3, -4)
b'\xa3\xff\xfc'
>>> unpack('u1u3u4s16', b'\xa3\xff\xfc')
(1, 2, 3, -4)
>>> calcsize('u1u3u4s16')
24

The unpacked fields can be named by assigning them to variables or by wrapping the result in a named tuple:

>>> from bitstruct import *
>>> from collections import namedtuple
>>> MyName = namedtuple('myname', [ 'a', 'b', 'c', 'd' ])
>>> unpacked = unpack('u1u3u4s16', b'\xa3\xff\xfc')
>>> myname = MyName(*unpacked)
>>> myname
myname(a=1, b=2, c=3, d=-4)
>>> myname.c
3

An example of packing/unpacking a unsinged integer, a signed integer, a float, a boolean, a byte string and a string:

>>> from bitstruct import *
>>> pack('u5s5f32b1r13t40', 1, -1, 3.75, True, b'\xff\xff', u'hello')
b'\x0f\xd0\x1c\x00\x00?\xffhello'
>>> unpack('u5s5f32b1r13t40', b'\x0f\xd0\x1c\x00\x00?\xffhello')
(1, -1, 3.75, True, b'\xff\xf8', u'hello')
>>> calcsize('u5s5f32b1r13t24')
80

The same format and values as in the previous example, but using LSB (Least Significant Bit) first instead of the default MSB (Most Significant Bit) first:

>>> from bitstruct import *
>>> pack('<u5s5f32b1r13', 1, -1, 3.75, True, b'\xff\xff')
b'\x87\xc0\x00\x03\x80\xbf\xff'
>>> unpack('<u5s5f32b1r13', b'\x87\xc0\x00\x03\x80\xbf\xff')
(1, -1, 3.75, True, b'\xff\xf8')
>>> calcsize('<u5s5f32b1r13')
56

An example of unpacking values from a hexstring and a binary file:

>>> from bitstruct import *
>>> unpack('s17s13r24', '0123456789abcdef'.decode('hex'))
(582, -3751, b'\xe2j\xf3')
>>> with open("test.bin", "rb") as fin:
...     unpack('s17s13r24', fin.read(8))
...
...
(582, -3751, b'\xe2j\xf3')

Change endianness of the data with byteswap(), and then unpack the values:

>>> from bitstruct import *
>>> packed = pack('u1u3u4s16', 1, 2, 3, 1)
>>> unpack('u1u3u4s16', byteswap('12', packed))
(1, 2, 3, 256)

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