Hello world with Genetic algorithm

genalg.py

# -*- coding: utf-8 -*-
"""
Hello world with Genetic algorithm
"""

import random

#Generate random string with same lenght that target
def initialization(target, letters):
    string = []
    string.extend(random.sample(letters, len(target)))
    return ''.join(string)

#Return a sum with the corrects letters of target
def fitness(string, target):
    sum = 0
    for i in range(len(string)):
        if(string[i] == target[i]):
            sum +=1
    return sum

#Add an random letter from letters to string
def mutate(parent, letters):
    index = random.randrange(0, len(parent))
    aux = list(parent)
    letter = random.sample(letters, 1)
    aux[index] = letter[0]
    return ''.join(aux)


def main():
    letters = " abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!."
    target = "Hello World!" 
    parent = initialization(target, letters)
    fit = fitness(parent, target)  
    while target != parent:
        child = mutate(parent, letters)
        childFit = fitness(child, target)
        if fit >= childFit:
            continue
        print(child)
        parent = child
        fit = childFit
        
if __name__ == '__main__':
    main()