CODEWITHSUNDEEP
pythonpython-3.xhexasciichecksum
Purgoufr
Purgoufr

Reputation: 982

calculate checksum hex in Python 3

I want to calculate checksum. The process I want to do like below;

Step-1

a="10F8000041303131303030353000000000000000"

Step-2

10+F8+00+00+41+30+31+31+30+30+30+35+30+00+00+00+00+00+00+00 = D0

Step-3

~D0 = 2F -> 2F + 1 = 30

I tried that;

def calc_checksum_two(s):        
return '%2X' % (-(sum(ord(c) for c in s) % 256) & 0xFF)
print(calc_checksum_two(a))

Result;

3D

Upvotes: 0

Views: 3978

Answers (2)

izzulmakin
izzulmakin

Reputation: 604

with s="10F8000041303131303030353000000000000000, sum(ord(c) for c in s) will sum each ord value of each character. This will sums [ord('1'), ord('0'), ord('F'), ...]. This is not what you wanted.

to build array of bytes from that string you should instead using:

[ a[i:i+2]] for i in range(0, len(a), 2) ]

this will create an array like this: ['10', 'F8', '00', ...]

Then to convert string hex/base16 to integer use int(hex_string,16)

That should do it, but here is the function

def calc_checksum_two(a):
    return hex(((sum(int(a[i:i+2],16) for i in range(0, len(a), 2))%0x100)^0xFF)+1)[2:]

Upvotes: 1

John Zwinck
John Zwinck

Reputation: 249592

b = [a[i:i+2] for i in range(0, len(a), 2)] # ['10', 'F8', '00', ...
c = [int(i, 16) for i in b] # [16, 248, 0, ...
d = 256 - sum(c) % 256 # 0x30
e = hex(d)[2:] # '30'

Upvotes: 2

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