Il Fri, 06 Mar 2009 10:19:22 +0000, mattia ha scritto:
> Hi, I'm new to python, and as the title says, can I improve this snippet
> (readability, speed, tricks):
>
> def get_fitness_and_population(fitness, population):
> return [(fitness(x), x) for x in population]
>
> def selection(fitness, population):
> '''
> Select the parent chromosomes from a population according to their
> fitness (the better fitness, the bigger chance to be selected) '''
> selected_population = []
> fap = get_fitness_and_population(fitness, population) pop_len =
> len(population)
> # elitism (it prevents a loss of the best found solution) # take the
> only 2 best solutions
> elite_population = sorted(fap)
> selected_population += [elite_population[pop_len-1][1]] +
> [elite_population[pop_len-2][1]]
> # go on with the rest of the elements for i in range(pop_len-2):
> # do something
Great, the for statement has not to deal with fap anymore, but with
another sequence, like this:
def get_roulette_wheel(weight_value_pairs):
roulette_wheel = []
for weight, value in weight_value_pairs:
roulette_wheel += [value]*weight
return roulette_wheel
def selection(fitness, population):
...
rw = get_roulette_wheel(fap)
for i in range(pop_len-2):
selected_population += [choice(rw)]
return selected_population
I think that using [choice(rw)]*len(fap) will produce the same sequence
repeted len(fap) times...
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