Stack own implementation..

Stack.py

class Stack:

    def __init__(self, maximum = 0):
        self.__currentIdx = -1
        self.__list = list()
        self.__maximum = maximum

    def push(self, newElement):
        if(self.__currentIdx + 1 < self.__maximum or self.__maximum == 0):
            self.__currentIdx += 1
            self.__list += [newElement]
        else:
            raise Exception("This stack's maximum is {0}, but current size is {1}".format(self.__maximum, self.__currentIdx + 1))
            
    def pop(self):
        if(self.__currentIdx > -1):
            res = self.__list[self.__currentIdx]
            del self.__list[self.__currentIdx]
            self.__currentIdx -= 1
            return res
        else:
            return None
    
    def size(self):
        return self.__currentIdx + 1