Roulette Wheel Selection in Python

Question

I tried to implement roulette wheel selection in python. I am confused to implement it. Here's my code; I hope someone can help me.

    fitness = [ind.fitness for ind in self.population] 
    total_fit = float(sum(fitness))
    relative_fitness = [f/total_fit for f in fitness]
    probabilities = [sum(relative_fitness[:i+1]) 
                 for i in range(len(relative_fitness))]
    
    print("population : ",self.population)
    print("end")
    new_pop = []

    for n in range(len(self.population)):
        r = random.random()
        for (i, individual) in self.population[n]:
            if r <= probabilities[i]:
                new_pop.append(individual)
                break

    print("new_pop")
    print(new_pop)

my error

this is my traceback error

     TypeError                                 Traceback (most recent call 
     last)
     <ipython-input-18-1ad9ce8eb687> in <module>
       19 
       20     while generation.generation_number < number_generation:
  ---> 21         generation.generate()
       22         if generation.generation_number == number_generation:
       23             # Last generation is the phase

     <ipython-input-17-ed4b4c1175ed> in generate(self)
       92         for n in range(len(self.population)):
       93             r = random.random()
  ---> 94             for (i, individual) in self.population[n]:
       95                 if r <= probabilities[i]:
       96                     new_pop.append(individual)

     TypeError: 'Organism' object is not iterable

Answer 1

Your inner loop doesn't make any sense. You're iterating on a single population member, and then trying to unpack it into a pair of values. I don't think either of those things will work.

I think you want for i, individual in enumerate(self.population), with enumerate added and without the indexing by [n].