python - 如何使字典在类实异常(exception)部不可变但在 python 中的类实例内部可变

Question

我的目标是创建具有独立身份、性别和州等属性的个体群体。人口被定义为一个类别。然后我创建了一个人口类实例，它允许我使用以下方法向人口中添加个人或从人口中删除个人:

class PopulationClass(object):

    def __init__(self):
        self.__population = dict()
        self.__iid_counter = 0
        self.__removed_individuals = []

    def add2population(self, no2add):
        import random

        iid_counter = self.__iid_counter

        for a in range(no2add):
            self.__population[iid_counter] = (iid_counter, random.sample(('F', 'M'), 1)[0], 'S')

            iid_counter += 1  

        self.__iid_counter = iid_counter

    def remove_from_population(self, key):
        self.__removed_individuals.append(self.__population.pop(key))

在终端中，我执行以下操作:

>>> population_instance = PopulationClass()
>>> population_instance.add2population(5)
>>> population_instance._PopulationClass__population
{0: (0, 'F', 'S'), 1: (1, 'M', 'S'), 2: (2, 'F', 'S'), 3: (3, 'M', 'S'), 4: (4, 'M', 'S')}
>>> population = population_instance._PopulationClass__population
>>> population[5] = 'Illegal changes'
>>> population
{0: (0, 'F', 'S'), 1: (1, 'M', 'S'), 2: (2, 'F', 'S'), 3: (3, 'M', 'S'), 4: (4, 'M', 'S'), 5:     'Illegal changes'}
>>> population_instance._PopulationClass__population
{0: (0, 'F', 'S'), 1: (1, 'M', 'S'), 2: (2, 'F', 'S'), 3: (3, 'M', 'S'), 4: (4, 'M', 'S'), 5: 'Illegal changes'}

我希望 population 会引用字典 (population_instance._PopulationClass__population) 并且不能对该字典进行更改。

但是，我希望使用 add2population 和 remove_from_population 方法向 population_instance 添加和删除个人。我怎样才能避免将此类非法更改传递给类实例？

Answer 1

你应该为访问私有(private)成员创建“get”函数

class PopulationClass(object):
  def __init__(self):
    self.__population = dict()
    self.__iid_counter = 0
    self.__removed_individuals = []
  def add2population(self, no2add):
    import random
    iid_counter = self.__iid_counter
    for a in range(no2add):
      self.__population[iid_counter] = (iid_counter, random.sample(('F', 'M'), 1)[0], 'S')
      iid_counter += 1  
    self.__iid_counter = iid_counter
  def remove_from_population(self, key):
    self.__removed_individuals.append(self.__population.pop(key))
  def getPopulation():
    import copy
    return copy.deepcopy(self.__population)

population_instance = PopulationClass()
population_instance.add2population(5)
population_instance._PopulationClass__population
population = population_instance.getPopulation()
population[5] = 'Illegal changes'
population
population_instance._PopulationClass__population