class manyData:
    def __init__(self, lstData):
        self.__data = lstData
    def push(self, val):
        self.__data.append(val)
        return self
    def pop(self):
        popVal = self.__data[-1]
        self.__data.pop()
        return popVal
    def __len__(self):
        return len(self.__data)

myData = manyData([1,2,3])
myData.push(100)
print(len(myData))
print(myData.peek())
print(myData.pop())