How to XOR two binary strings in python

Question

I need to do XOR operation between two binary strings.

xor("00110011", "11001100") = "11111111"

i am currently using this function

def xor(x, y):
    ans = ""
    for i in xrange(len(x)):
        if x[i] == "0" and y[i] == "1" or x[i] == "1" and y[i] == "0":
            ans += "1"
        else:
            ans += "0"
    return ans

please give me good method

You can use parenthesis, if you like. BTW, is there a specific problem in this code? — thefourtheye
– thefourtheye, Commented Jul 5, 2016 at 13:22
Please edit your question and include a sample of your input and the expected output. — user5547025
– user5547025, Commented Jul 5, 2016 at 13:24
you can use ^ - the xor operator. Please see stackoverflow.com/questions/19414093/… — gunzapper
– gunzapper, Commented Jul 5, 2016 at 13:25
If you are using Python 3, these are not binary strings in the Python sense. — user5547025
– user5547025, Commented Jul 5, 2016 at 13:32
You need to tell us about edge-cases too. What happens with with xor('01', '00') for example? Is the output '1' or '01'. In other words, should the output be the same string length, always? — Martijn Pieters
– Martijn Pieters, Commented Jul 5, 2016 at 13:35

Martijn Pieters · Accepted Answer · 2016-07-05 13:33:20Z

6

If you must use strings of '0' and '1' characters, just use a mapping:

_xormap = {('0', '1'): '1', ('1', '0'): '1', ('1', '1'): '0', ('0', '0'): '0'}
def xor(x, y):
    return ''.join([_xormap[a, b] for a, b in zip(x, y)])

otherwise, just convert to two integers, XOR those and re-format back to a binary string:

def xor(x, y):
    return '{1:0{0}b}'.format(len(x), int(x, 2) ^ int(y, 2))

This ensures that the resulting string has the same length by zero-padding to the length of x.

edited Jul 5, 2016 at 13:33

answered Jul 5, 2016 at 13:26

Martijn Pieters

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Community · Accepted Answer · 2017-05-23 12:08:03Z

4

def xor(x, y):
    return '{0:b}'.format(int(x, 2) ^ int(y, 2))

Credits to this answer. Contrary to popular belief, Python does have bitwise operators.

edited May 23, 2017 at 12:08

CommunityBot

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answered Jul 5, 2016 at 13:25

Nee

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1 Comment

Martijn Pieters Over a year ago

Note that this can lead to a shorter binary string, the null-padding is lost. Try it with xor('00000001', '00000000') for example.

gunzapper · Accepted Answer · 2016-07-05 13:42:48Z

-2

If you need to reinvent the whell

def alternative_xor(x, y):
  a = int(x)
  b = int(y)  
  return (a & ~b) | (~a & b)

edited Jul 5, 2016 at 13:42

answered Jul 5, 2016 at 13:37

gunzapper

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2 Comments

Martijn Pieters Over a year ago

The return value must be a string too. But why so circumspect about using ^?

gunzapper Over a year ago

In addition: I like your use of the map! ^_^

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