Python - 'type' object is not subscriptable

import genetic_algorithm

def main():

    ga = genetic_algorithm.GeneticAlgorithm(100, 0.001, 0.95, 0)

    population = ga.initPopulation(50)

    ga.evalPopulation(population)

    generation = 1

    while ga.isTerminationConditionMet(population) == false:

        print("Best solution", population.getFittest(0).toString())

        population = ga.crossoverPopulation(population)

        population = ga.mutatePopulation(population)

        ga.evalPopulation(population)

        generation += 1

    print("Found solution in ", generation, " generations")

    print("Best solution:", population.getFittest(0).toString())

if __name__ == "__main__":

    main()

class GeneticAlgorithm:

    def __init__(self, populationSize, mutationRate, crossoverRate, elitismCount):

        self.populationSize=populationSize

        self.mutationRate=mutationRate

        self.crossoverRate=crossoverRate

        self.elitismCount=elitismCount

    def initPopulation(self,chromosomeLength):

        population = population_file.Population(self.populationSize, chromosomeLength)

        return population

    def calcFitness(self, individual):

        correctGenes = 0

        for geneIndex in range (0,individual.getChomosomeLength()):

            if individual.getGene(geneIndex)==1:

                correctGenes +=1

        fitness= correctGenes/individual.getChomosomeLength()

        individual.setFitness(fitness)

        return fitness

       .......

import individual_file

import random

class Population:

    def __init__(self,populationSize):

        self.populationSize=individual_file[populationSize]

    def __init__(self,populationSize,chromosomeLength):

        self.population = individual_file.Individual[populationSize]

        for individualCount in range (0,populationSize):

            individual = individual_file.Individual(chromosomeLength)

            self.population[individualCount]= individual

    def getIndividuals(self):

        return self.population

    def getFittest(self,offset):

        for i in range (0,population.size()):

            for j in range (0, population.size()):

                o1= self.population[i]

                if self.population[j-1].getFitness()<self.population[j].getFitness():

                    temp = self.population[j-1]

                    self.population[j-1]=self.population[j]

                    self.population[j]=temp

        return self.population[offset]

        .........