Python栈类继承问题求助：子类继承父类属性触发TypeError

Hey there! Let's break down what's causing the TypeError in your code and fix it step by step.

What's Going Wrong? #

Your error stems from three key issues in the Stack3 subclass implementation:

1. Missing required argument when creating Stack3 instance
   You defined Stack3.__init__() with a mandatory __list parameter, but tried to create an instance with s = Stack3() (no arguments passed). This directly triggers the "missing positional argument" error.

2. Incorrect parent constructor call
   The parent Stack class's __init__() method takes no arguments (other than self), but you're calling super().__init__(self.__list) which passes an extra parameter—this would cause another error even if you did supply __list.

3. Unnecessary private variable redefinition
   In Python, double-underscore variables undergo name mangling: the parent's __list becomes _Stack__list, while your subclass's __list becomes _Stack3__list—these are two separate variables. You don't need to redefine this list, since the parent class already initializes it.

Fixed Code #

Here's the corrected version of your Stack3 class and usage code:

class Stack:
    def __init__(self):
        self.__list= []
    def isEmpty(self):
        return self.__list == []
    def size(self):
        return len(self.__list)
    def clear(self):
        self.__list.clear()
    def push(self, item):
        self.__list.append(item)
    def pop(self):
        if self.isEmpty():
            return None
        else:
            return self.__list.pop()
    def get(self):
        if self.isEmpty():
            return None
        else:
            return self.__list[-1]
    def __str__(self):
        output = '<'
        for i in range( len(self.__list) ):
            item = self.__list[i]
            if i < len(self.__list)-1 :
                output += f'{str(item)}, '
            else:
                output += f'{str(item)}'
        output += '>'
        return output

class Stack3(Stack):
    def __init__(self):
        # Call parent constructor to initialize the underlying list
        super().__init__()
    
    def printMe(self):
        # Actually print the string generated by the parent's __str__ method
        print(super().__str__())

s = Stack3()
print(s.pop())
for i in range(1,6):
    s.push(i)
print('Content of stack =',s)
print('Item at top=',s.get())
print('Size=', s.size())
while not s.isEmpty():
    print(s.pop())
print(s)

Key Changes Explained #

• Simplified Stack3.__init__(): Removed the __list parameter and called super().__init__() without arguments, letting the parent class handle initializing the empty list.
• Fixed printMe(): The original code called super().__str__() but didn't do anything with the resulting string—now it prints it directly.
• Proper inheritance: Stack3 now correctly inherits all the functionality from Stack without overriding or redefining unnecessary variables.

Expected Output #

When you run the fixed code, you'll get this output:

None
Content of stack = <1, 2, 3, 4, 5>
Item at top= 5
Size= 5
5
4
3
2
1
<>

内容的提问来源于stack exchange，提问作者rageyboi123