使用@property+setter封装账户编号时触发无限递归的原因？

你遇到的无限递归问题，根源在于@property的实现逻辑错误，没有区分属性的实际存储变量和访问器方法：

问题代码 #

class SingleBankAccount:
    
    def __init__(self, account_number, account_balance):
        self.account_number = account_number
        self.account_balance = account_balance
        
    @property
    def account_number(self):
        return self.account_number
        
    @account_number.setter
    def account_number(self, number):
        # if there is a number already, raise exception, otherwise set it
        if self.account_number:
            raise AccountException("Someone tried to change the account number!")
        else:
            self.account_number = number

报错信息 #

File "main.py", line 17, in account_number

    if self.account_number:

  File "main.py", line 13, in account_number

    return self.account_number

  File "main.py", line 13, in account_number

    return self.account_number

  File "main.py", line 13, in account_number

    return self.account_number

  [Previous line repeated 993 more times]

RecursionError: maximum recursion depth exceeded

递归原因详解 #

• Getter方法的无限递归
  当你用@property装饰account_number方法后，self.account_number不再是直接访问实例属性，而是会调用这个getter方法。而你的getter里写了return self.account_number，这会再次调用getter方法，形成无限循环，直到触发Python的递归深度限制。

• Setter方法的双重递归
  在setter方法中存在两处递归触发点：

  • 判断if self.account_number:时，会调用getter方法，再次进入递归循环
  • 执行self.account_number = number时，会调用setter方法本身，同样形成递归

本质问题是：你没有用一个独立的变量来存储account_number的实际值，而是直接在getter/setter里操作同名的"属性"，而这个"属性"其实是被@property包装后的方法，导致每次访问或赋值都在调用方法自身。

修复方案 #

使用下划线开头的私有变量（比如_account_number）存储实际值，getter和setter操作这个私有变量，避免递归：

class AccountException(Exception):
    pass

class SingleBankAccount:
    
    def __init__(self, account_number, account_balance):
        self._account_number = account_number
        self.account_balance = account_balance
        
    @property
    def account_number(self):
        return self._account_number
        
    @account_number.setter
    def account_number(self, number):
        if self._account_number:
            raise AccountException("Someone tried to change the account number!")
        else:
            self._account_number = number

这样外部通过account_number属性访问时，会自动调用getter/setter，而内部存储用_account_number，不会触发递归，同时实现了禁止修改账号的需求。

内容的提问来源于stack exchange，提问作者Alejandro Veintimilla