Python OOP类属性赋值后返回None问题排查及优化建议

你的Burrito类属性返回None的核心原因有两个：

• 你的setter方法没有显式返回值，Python中无return语句的函数默认返回None，而你把这个返回值赋值给了self.meat、self.rice、self.beans，导致这些属性最终被覆盖为None。
• 更混乱的是，setter方法内部已经直接修改了self的对应属性（比如self.meat = attribute），但随后又被self.meat = self.setter(...)的返回值（None）覆盖，等于白做了内部赋值。

比如创建vegg_burrito时，setter里已经把self.meat设为"tofu"，但紧接着self.meat = self.setter(...)把它改成了None。

有两种清晰的修复方式，选其一即可：

方式1：让setter返回处理后的值，不在内部修改self #

修改setter方法，只负责验证并返回正确值，由__init__赋值给属性：

BEANS = ["black", "pinto"]
RICES = ["brown", "white"]
MEATS = ["chicken", "pork", "steak", "tofu"]

class Burrito:
    def __init__(self,
                 meat,
                 to_go,
                 rice,
                 beans,
                 extra_meat=False,
                 guacamole=False,
                 cheese=False,
                 pico=False,
                 corn=False
                 ):
        # 用setter的返回值赋值
        self.meat = self.setter("meat", meat)
        self.rice = self.setter("rice", rice)
        self.beans = self.setter("beans", beans)
        # 修复：使用传入的to_go参数，而非硬编码为False
        self.to_go = to_go
        self.extra_meat = extra_meat
        self.guacamole = guacamole
        self.cheese = cheese
        self.pico = pico
        self.corn = corn

    def setter(self, category, attribute):
        if category == "meat":
            return attribute if attribute in MEATS else False
        elif category == "rice":
            return attribute if attribute in RICES else False
        elif category == "beans":
            return attribute if attribute in BEANS else False
        else:
            return "Error"

方式2：setter直接修改self属性，调用时不需要赋值 #

__init__里直接调用setter，不接收返回值，由setter完成属性设置：

BEANS = ["black", "pinto"]
RICES = ["brown", "white"]
MEATS = ["chicken", "pork", "steak", "tofu"]

class Burrito:
    def __init__(self,
                 meat,
                 to_go,
                 rice,
                 beans,
                 extra_meat=False,
                 guacamole=False,
                 cheese=False,
                 pico=False,
                 corn=False
                 ):
        # 直接调用setter设置属性，不需要赋值
        self.setter("meat", meat)
        self.setter("rice", rice)
        self.setter("beans", beans)
        self.to_go = to_go
        self.extra_meat = extra_meat
        self.guacamole = guacamole
        self.cheese = cheese
        self.pico = pico
        self.corn = corn

    def setter(self, category, attribute):
        if category == "meat":
            self.meat = attribute if attribute in MEATS else False
        elif category == "rice":
            self.rice = attribute if attribute in RICES else False
        elif category == "beans":
            self.beans = attribute if attribute in BEANS else False
        else:
            setattr(self, category, "Error")

• 用类变量统一管理可选值：把BEANS、RICES、MEATS定义为类属性，更符合OOP封装原则：

  class Burrito:
      BEANS = ["black", "pinto"]
      RICES = ["brown", "white"]
      MEATS = ["chicken", "pork", "steak", "tofu"]
      
      # 其余代码...
  

• 拆分验证逻辑，避免臃肿的setter：用字典映射简化setter，减少重复代码：

  def setter(self, category, attribute):
      valid_options = {
          "meat": self.MEATS,
          "rice": self.RICES,
          "beans": self.BEANS
      }
      if category in valid_options:
          setattr(self, category, attribute if attribute in valid_options[category] else False)
      else:
          setattr(self, category, "Error")
  

• 使用@property实现属性验证（进阶）：如果需要后续修改属性时也能自动验证，可以用@property装饰器：

  class Burrito:
      BEANS = ["black", "pinto"]
      RICES = ["brown", "white"]
      MEATS = ["chicken", "pork", "steak", "tofu"]
      
      def __init__(self, meat, to_go, rice, beans, **kwargs):
          self._meat = None
          self._rice = None
          self._beans = None
          # 通过属性赋值触发验证
          self.meat = meat
          self.rice = rice
          self.beans = beans
          self.to_go = to_go
          # 批量处理可选参数
          for key, value in kwargs.items():
              setattr(self, key, value)
      
      @property
      def meat(self):
          return self._meat
      
      @meat.setter
      def meat(self, value):
          self._meat = value if value in self.MEATS else False
      
      # 同理实现rice和beans的@property和setter
  

内容的提问来源于stack exchange，提问作者bbartling