Python stud对象AttributeError：无number_of_students属性问题求助

原代码 #

class stud:

    def __init__(self) :
        try:    
            self.number_of_students = int(input("Enter number of students :\n"))
        except ValueError:
                print("Enter numerical value")
        finally:
                print(self.number_of_students)

obj1=stud()

问题现象 #

输入数值时程序正常运行；输入非数值内容时，除输出Enter numerical value外，还会抛出如下AttributeError异常：

AttributeError :
  File "e:\Data\Programming\Python!!!\OOP\tempCodeRunnerFile.py", line 14, in <module>
    obj1=stud()
         ^^^^^^
  File "e:\Data\Programming\Python!!!\OOP\tempCodeRunnerFile.py", line 9, in __init__
    print(self.number_of_students)
          ^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'stud' object has no attribute 'number_of_students'

原因分析 #

• self.number_of_students属性仅在try块执行成功（输入为有效数值）时才会被创建并赋值
• 输入非数值触发ValueError后，except块仅执行打印提示，不会给对象绑定number_of_students属性
• finally块是无论try/except是否执行成功都会强制运行的代码块，此时对象不存在number_of_students属性，因此打印时抛出AttributeError

解决方案 #

方案1：提前初始化属性默认值

在try块之前先给属性赋默认值，确保无论是否触发异常，属性都存在：

class stud:
    def __init__(self):
        self.number_of_students = 0  # 初始化默认值
        try:    
            self.number_of_students = int(input("Enter number of students :\n"))
        except ValueError:
            print("Enter numerical value")
        finally:
            print(self.number_of_students)

obj1=stud()

方案2：在finally块中检查属性是否存在

通过hasattr()函数判断属性是否存在，避免直接访问不存在的属性：

class stud:
    def __init__(self):
        try:    
            self.number_of_students = int(input("Enter number of students :\n"))
        except ValueError:
            print("Enter numerical value")
        finally:
            if hasattr(self, 'number_of_students'):
                print(self.number_of_students)
            else:
                print("未输入有效数值")

obj1=stud()

方案3：在except块中给属性赋值

异常触发时也给属性赋一个占位值（比如None），保证属性存在：

class stud:
    def __init__(self):
        try:    
            self.number_of_students = int(input("Enter number of students :\n"))
        except ValueError:
            print("Enter numerical value")
            self.number_of_students = None  # 异常时赋值为None
        finally:
            print(self.number_of_students)

obj1=stud()

内容的提问来源于stack exchange，提问作者ZulQarnain