docs: def initialize_pop(self):
          """Assigns initial fitnesses."""
          self.toolbox.register("individual", self.generate)
          self.toolbox.register("population", tools.initRepeat,
                                list, self.toolbox.individual)
          self.population = self.toolbox.population(n=self._params['popsize'])
          self.assign_fitnesses(self.population)
          self._params['model_count'] += len(self.population)