Question

I am reading a file (disk images and /dev/sda and likes) in python using binary mode. I am reading the first sector (512 bytes) and am trying to print disk information (ref: Wikipedia Articles).

To interpret things like the 32bit LBA of first absolute sector in the partition, I am doing things like –

def int32(bytes):
    return int(bytes[3]<<24|bytes[2]<<16|bytes[1]<<8|bytes[0])

def int16(bytes):
    return int(bytes[1]<<8|bytes[0])

print('LBA:',int32(partitionEntry[8:12]))

Is there native wat to do this in python? As typecasting intVar=(int*)someBasePointer in C

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Added after marking as answered:

Is there a way to do this for odd bit structure? Like the CHS. C (cylinders) are 10 bits 8 bits from one byte and 2 from the other byte. My current approach for this is

def getCHS(bytes):
    c=bytes[1]&3<<8|bytes[2]
    h=bytes[0]
    s=bytes[1]&63
    return {'c':c,'s':s,'h':h}

Answer 1

You want the struct.unpack() function.

import struct

def int32(some_bytes):
    return struct.unpack("i", some_bytes)[0]

def int16(some_bytes):
    return struct.unpack("h", some_bytes)[0]

If you’re reading from a system that uses different endian values than the current system, you may need to specify the endianness in the format string as well.

(i and h are the signed int versions; if you want unsigned, use I and H)