Modification to Hamming distance/ Edit Distance

Question

I am having trouble modifying the Hamming distance algorithm in order to affect my data in two ways

1. Add .5 to the Hamming distance if a capital letter is switched for a lower case letter unless it is in the first position.
   Examples include: "Killer" and "killer" have a distance of 0 "killer" and "KiLler" have a Hamming distance of .5. "Funny" and FAnny" have a distance of 1.5 (1 for the different letter, additional .5 for the different capitalization).

2. Making it so that b and d (and their capitalized counterparts) are seen as the same thing

Here is the code i have found that makes up the basic Hamming program

def hamming_distance(s1, s2):
    assert len(s1) == len(s2)
    return sum(ch1 != ch2 for ch1, ch2 in zip(s1, s2))

if __name__=="__main__":
    a = 'mark'
    b = 'Make'
    print hamming_distance(a, b) 

Any suggestions would be welcomed!

Answer 1

Here is a simple solution. For sure it could be optimized for better performance.

Note: I used Python 3, since Python 2 will retire soon.

def hamming_distance(s1, s2):
    assert len(s1) == len(s2)
    # b and d are interchangeable
    s1 = s1.replace('b', 'd').replace('B', 'D')
    s2 = s2.replace('b', 'd').replace('B', 'D')
    # add 1 for each different character
    hammingdist = sum(ch1 != ch2 for ch1, ch2 in zip(s1.lower(), s2.lower()))
    # add .5 for each lower/upper case difference (without first letter)
    for i in range(1, len(s1)):
        hammingdist += 0.5 * (s1[i] >= 'a' and s1[i] <= 'z' and\
                              s2[i] >= 'A' and s2[i] <= 'Z' or\
                              s1[i] >= 'A' and s1[i] <= 'Z' and\
                              s2[i] >= 'a' and s2[i] <= 'z')
    return hammingdist

def print_hamming_distance(s1, s2):
    print("hamming distance between", s1, "and", s2, "is",
          hamming_distance(s1, s2))

if __name__ == "__main__":
    assert hamming_distance('mark', 'Make') == 2
    assert hamming_distance('Killer', 'killer') == 0
    assert hamming_distance('killer', 'KiLler') == 0.5
    assert hamming_distance('bole', 'dole') == 0
    print("all fine")
    print_hamming_distance("organized", "orGanised")
    # prints: hamming distance between organized and orGanised is 1.5