Создание исключения

import operator


class Stack:
    def __init__(self):
        self._stack = []

    def push(self, num):
        return self._stack.append(num)

    def pop(self):
        try:
            return self._stack.pop()
        except IndexError:
            raise IndexError('Empty')


OPERATORS = {
    '+': operator.add,
    '-': operator.sub,
    '*': operator.mul,
    '/': operator.floordiv
 }


class Calculator:
    def __init__(self, array, operators=None):
        self._array = array
        self._operators = operators

    def calculation(self, stack=None):
        stack = Stack() if stack is None else stack
        for item in self._array:
            if item in self._operators:
                second_num = stack.pop()
                first_num = stack.pop()
                stack.push(self._operators[item](first_num, second_num))
            else:
                try:
                    stack.push(int(item))
                except ValueError as error:
                    raise ValueError(f'{error} - Item is not num!')
        return stack.pop()


if __name__ == '__main__':
    array = input().split()
    stack = Stack()
    print(Calculator(array, OPERATORS).calculation(stack))

Помогите создать свое исключение вместо:

except IndexError:
    raise IndexError('Empty')