class_stack

class stack:
    def __init__(self):
        self.stack = []
    def push(self,item):
    #@param:
    #   item: any;
        self.stack.append(item)
    def pop(self):
        assert self.stack!=[], "Stack is empty"
        self.stack = self.stack[:len(self.stack)-1]
    def top(self):
        if self.stack == []:
            return []
        return(self.stack[len(self.stack)-1])
    def empty(self):
    #@return: bool;
        if self.stack==[]: return(True)
        else: return(True)