ValueError：在处理上述异常期间，位数必须大于零，否则会发生另一个异常

Question

我正在尝试实现遗传算法，程序在第一代后终止。。不知道为什么。。代码如下。。提出的异常是。。

文件"C：\用户\伊山\AppData\本地\程序\Python\Python36\lib\random.py"，第255行，选择i=自己。_randbelow（len（seq））文件"C：\用户\伊山\AppData\本地\程序\Python\Python36\lib\random.py"，第232行，_randbelowr=getrandbit（k）#0

在处理上述异常期间，发生了另一个异常：

回溯（最后一次调用）：文件“C:/Users/Eshan/Desktop/model/simple_ga.py”，第87行，ga（）文件“C:/Users/Eshan/Desktop/model/simple_ga.py”，第32行，ga代理=交叉（代理）文件“C:/Users/Eshan/Desktop/model/simple_ga.py”，第62行，交叉父1=随机选择（代理）文件“C:\Users\Eshan\AppData\Local\Programs\Python\Python36\lib\random.py”，第257行，在选项raise INDEXROR（“不能从空序列中选择”）中，INDEXROR:不能从空序列中选择

进程已完成，退出代码为1

from fuzzywuzzy import fuzz
import random
import string


class Agent:
    def __init__(self, length):

        self.string = ''.join(random.choice(string.ascii_letters) for _ in range(length))
        self.fitness = -1

    def __str__(self):
        return 'String: ' + str(self.string) + ' Fitness: ' + str(self.fitness)


in_str = 'string-python'
in_str_len = len(in_str)
population = 20
generations = 1000


def ga():

    agents = init_agents(population, in_str_len)

    for generation in range(generations):

        print('Generation: ' + str(generation))

        agents = selection(agents)
        agents = fitness(agents)
        agents = crossover(agents)
        agents = mutation(agents)

        if any(agent.fitness >= 90 for agent in agents):
            print('Threshod met!')
            exit(0)


def init_agents(population, length):
    return [Agent(length) for _ in range(population)]


def fitness(agents):
    for agent in agents:
        agent.fitness = fuzz.ratio(agent.string, in_str)

    return agents


def selection(agents):

    agents = sorted(agents, key=lambda agent: agent.fitness, reverse=True)
    print('\n'.join(map(str, agents)))
    agents = agents[:int(0.2 * len(agents))]
    return agents


def crossover(agents):
    offspring = []
    for _ in range(int((population - len(agents)) / 2)):
        parent1 = random.choice(agents)
        parent2 = random.choice(agents)
        child1 = Agent(in_str_len)
        child2 = Agent(in_str_len)
        split = random.randint(0, in_str_len)
        child1.string = parent1.string[0:split] + parent2.string[split:in_str_len]
        child2.string = parent2.string[0:split] + parent1.string[split:in_str_len]
        offspring.append(child1)
        offspring.append(child2)

    return agents


def mutation(agents):

    for agent in agents:
        for idx, param in enumerate(agent.string):
            if random.uniform(0.0, 1.0) <= 0.1:
                agent.string = agent.string[0:idx] + random.choice(string.ascii_letters) + agent.string[idx+1:in_str_len]

    return agents

if __name__ == '__main__':
    in_str = 'string-python'
    in_str_len = len(in_str)
    ga()

Answer 1

看起来您的代理是空的，因此当您执行parent1=random.choice（agents）时，会出现您看到的错误，因为您无法从空列表中进行随机选择。