Roulette wheel

[Peter Otten]

mattia wrote:

> The last question: how can I improve readability in this piece of code?
> 
> def crossover(pop, prob=0.6):
>     """
>     With a crossover probability cross over the parents to form new
>     offspring. If no crossover was performed, offspring is the exact copy
>     of parents. """
>     cpop = []
>     for i in range(0, len(pop), 2):
>         # crossover
>         if prob > random():
>             crossover_point = randint(0, len(pop[i])-1)
>             nchromosome1 = pop[i][:crossover_point] +
>             pop[i+1][crossover_point:] nchromosome2 =
>             pop[i+1][:crossover_point] + pop[i][crossover_point:]
>         else:
>             nchromosome1 = pop[i][:]
>             nchromosome2 = pop[i+1][:]

>         cpop += [nchromosome1] + [nchromosome2]

I'd write that as 

cpop.append(nchromosome1)
cpop.append(nchromosome2)

thus avoiding the intermediate lists.

>     return cpop
> 
> And with this one my example is complete!

Just for fun here's an alternative version of your function

def generate_crossover(pop, prob):
    for a, b in zip(*[iter(pop)]*2):
        if prob > random():
            cut = randrange(len(a))
            a, b = a[:cut] + b[cut:], b[:cut] + a[cut:]
        yield a
        yield b
            
def crossover(pop, prob=0.6):
    return list(generate_crossover(pop, prob))

but as the original is a bit clearer I recommend that you stick with it.

Peter