hellogen.py

import random, string

GA_POPSIZE = 2048
GA_ELITRATE= 0.10 # elitism rate
GA_MUTATIONRATE = 0.25 # mutation rate
GA_TARGET = "Hello world!"
GA_CHARS = string.letters + string.digits + string.punctuation + string.whitespace

def randstr():
    return "".join([random.choice(GA_CHARS) for i in xrange(len(GA_TARGET))])

def fitness(value):
    return sum([abs(ord(value[j]) - ord(GA_TARGET[j])) for j in xrange(len(GA_TARGET))])

def mate(population, buffer):
    esize = int(GA_POPSIZE * GA_ELITRATE)
    for i in xrange(esize): # Elitism
        buffer[i] = population[i]
    for i in range(esize, GA_POPSIZE):
        i1 = random.randint(0, GA_POPSIZE / 2)
        i2 = random.randint(0, GA_POPSIZE / 2)
        spos = random.randint(0, len(GA_TARGET))
        buffer[i] = population[i1][:spos] + population[i2][spos:] # Mate
        if random.random() < GA_MUTATIONRATE: # Mutate
            pos = random.randint(0, len(GA_TARGET)-1)
            buffer[i] = buffer[i][:pos] + random.choice(GA_CHARS) + buffer[i][pos+1:]

population = [randstr() for i in xrange(GA_POPSIZE)]
buffer = [randstr() for i in xrange(GA_POPSIZE)]
while True:
    population = sorted(population, key=lambda c: fitness(c))
    print "[%03d]\tBest (%04d)\t%s" % (i, fitness(population[0]), population[0])
    if not fitness(population[0]): # We're done, best match found
        break
    mate(population, buffer)
    population, buffer = buffer, population