how to implement bitwise XOR in python 3

Question

i would like to implement XOR operation of 1000000^10100001.

def keygen(key):
    print (key)
    k0 = key
    w0 = k0[0:8]
    w1 = k0[8:]

    w2 = int(w1) ^ int(10000000)

But im not getting the correct output. My w1 is:10100001 and my binary o.p w2 is:0b100110001011110110000010.

I should get: 00100001

If you want to use the number as a bitflag, make it binary with 0b100000 — BallpointBen
– BallpointBen, Commented Mar 6, 2017 at 17:19
i dont want bit flag, just need to implement XOR.. Any suggestion? — Goldy Tomy
– Goldy Tomy, Commented Mar 6, 2017 at 17:21

falsetru · Accepted Answer · 2017-03-06 17:39:47Z

1

You need to use 0b... to denote binary number.

Also when converting string to a number using int, specify base 2 (the second optional parameter). Otherwise it is interpreted as a decimal number:

w2 = int(w1, 2) ^ 0b10000000
#            ^    ^^------------ binary (= 128 in decimal)
#            |
#            optional argument (base 2)

And, you don't need to call int for 0b10000000, because it's already an int object.

UPDATE If you want to get a string representation back, use str.format or format with format specify 08b (0: leading zeros, 8: at least 8 digits, b: binary)

>>> format(w2, '08b')
00100001

edited Mar 6, 2017 at 17:39

answered Mar 6, 2017 at 17:22

falsetru

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9 Comments

Goldy Tomy Over a year ago

Thank you, it worked. One more question.. Is there a way to remove the bit flag? or do ive to convert to string and remove the 0b

falsetru Over a year ago

@GoldyTomy, binary 0b10000000 is decimal 128. So, you can replace the line with w2 = int(w1, 2) ^ 128

Goldy Tomy Over a year ago

my requirement is to use bits for my program, after the XOR operation i need to work with bits. Thats why i cant use 128. Moreover, if i change the input w1 to 10011010, my output becomes 0b11010, which is not eight bit output.

falsetru Over a year ago

@GoldyTomy, I don't get what you mean. Do you want result back as a string? then try bin(w2) (this will give you a string with a prefix 0b), format(w2, 'b'), format(w2, '08b') (at least 8 string with leading 0 if needed) or '{:08b}'.format(w2), ...

Goldy Tomy Over a year ago

so, what im looking is w2 = 10011010 ^ 10000000 and the output should also be 8 bit output in bits. the above format you gave is working but it just removes the 0 in front. Im working in a code which deals only with bits, so i guess i need to check the output and then append the missing zeros if there are any.

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