how to do bitwise exclusive or of two strings in python?

I would like to perform a bitwise exclusive or of two strings in python, but xor of strings are not allowed in python. How can I do it ?

You can convert the characters to integers and xor those instead:

l = [ord(a) ^ ord(b) for a,b in zip(s1,s2)]

Here's an updated function in case you need a string as a result of the XOR:

def sxor(s1,s2):    
    # convert strings to a list of character pair tuples
    # go through each tuple, converting them to ASCII code (ord)
    # perform exclusive or on the ASCII code
    # then convert the result back to ASCII (chr)
    # merge the resulting array of characters as a string
    return ''.join(chr(ord(a) ^ ord(b)) for a,b in zip(s1,s2))

See it working online: ideone

If you want to operate on bytes or words then you'll be better to use Python's array type instead of a string. If you are working with fixed length blocks then you may be able to use H or L format to operate on words rather than bytes, but I just used 'B' for this example:

>>> import array
>>> a1 = array.array('B', 'Hello, World!')
>>> a1
array('B', [72, 101, 108, 108, 111, 44, 32, 87, 111, 114, 108, 100, 33])
>>> a2 = array.array('B', ('secret'*3))
>>> for i in range(len(a1)):
    a1[i] ^= a2[i]


>>> a1.tostring()
';\x00\x0f\x1e\nXS2\x0c\x00\t\x10R'

For bytearrays you can directly use XOR:

>>> b1 = bytearray("test123")
>>> b2 = bytearray("321test")
>>> b = bytearray(len(b1))
>>> for i in range(len(b1)):
...   b[i] = b1[i] ^ b2[i]

>>> b
bytearray(b'GWB\x00TAG')