python without ifs. challenge one.

#coding: utf-8
"""
Make calculator that has [2, 3, 5] numbers, plus and minus buttons and equal button.

Additional condition: make it without any if statements
"""
class CalcModel:
    """
    Calculator Model

    >>> c = CalcModel()
    >>> c.add_number(5)
    >>> c.add_number(6)
    >>> c.current_number
    '056'
    >>> c.plus()
    >>> c.number_stack
    [56]
    >>> c.add_number(3)
    >>> c.add_number(4)
    >>> c.equal()
    90
    >>> c.add_number(6)
    >>> c.add_number(7)
    >>> c.minus()
    >>> c.equal()
    23
    """
    actions = {
        '+': lambda x,y: x+y,
        '-': lambda x,y: x-y
    }
    def __init__(self):
        self.current_number = "0"
        self.number_stack = []
        self.action_stack = []

    def add_number(self, n):
        self.current_number += str(n)

    def add_action(self, action):
        self.number_stack.append(int(self.current_number))
        self.current_number = "0"
        self.action_stack.append(action)

    def plus(self):
        self.add_action('+')

    def minus(self):
        self.add_action('-')

    def equal(self):
        self.number_stack.append(int(self.current_number))
        result = 0
        for ind, action in enumerate(self.action_stack):
            result += self.actions[action](self.number_stack[ind], self.number_stack[ind+1])
        self.current_number = "0"
        self.number_stack = [result]
        self.action_stack = []
        return result

if __name__ == "__main__":
    import doctest
    doctest.testmod()