function to find a duplicate element in a limited range list

1def findDuplicate(A):
2 
3    xor = 0
4 
5    # take xor of all list elements
6    for i in range(len(A)):
7        xor ^= A[i]
8 
9    # take xor of numbers from 1 to `n-1`
10    for i in range(1, len(A)):
11        xor ^= i
12 
13    # same elements will cancel each other as a ^ a = 0,
14    # 0 ^ 0 = 0 and a ^ 0 = a
15 
16    # `xor` will contain the missing number
17    return xor