使用Python列表作为存储实现一个栈 --栈

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使用Python列表作为存储实现一个栈 :

class ArrayStack:
    def __init__(self):
        # Create an empty stack
        self.__data = []

    def __len__(self):
        # Return the number of elements in the stack
        return len(self.__data)

    def is_empty(self):
        # Retutn True if the stack is empty
        return len(self.__data) == 0

    def push(self, e):
        # Add an element to the top of stack
        self.__data.append(e)

    def pop(self):
        # If element is empty ,it will raise Empty exception
        if self.is_empty():
            raise Empty('Stack is empty!')
        # Remove and return the element from the top of the stack
        return self.__data.pop()

    def top(self):
        # If element is empty ,it will raise Empty exception
        if self.is_empty():
            raise Empty('Stack is empty!')
        # Return the last item in the list
        return self.__data[-1]


class Empty(Exception):
    pass