Python Pi Generator

#!/usr/bin/python3

# Explained @ https://youtu.be/NaL_Cb42WyY
class Pi :
    _a: int
    _b: int
    _c: int

    __FIRST_C: int = 1

    def __gcd(self, a: int, b: int) -> int :
        while b :
            c = a % b
            a = b
            b = c
        return a

    def __simplify(self) :
        tmp = self.__gcd(self._a, self._b)
        self._a //= tmp
        self._b //= tmp

    def __init__(self) :
        self._a = 0
        self._b = 1
        self._c = self.__FIRST_C

    def get_num(self) -> int :
        return self._a

    def get_dom(self) -> int :
        return self._b

    def get_steps(self) -> int :
        return self._c

    def approximate(self) -> float :
        return self._a * 4 / self._b

    def step_forward(self) :
        num, dom, tmp = ((self._c % 2) * (-1 if (self._c + 1) % 4 == 0 else 1)), self._c, self._b
        self._a *= dom
        self._b *= dom
        num *= tmp
        self._a += num
        self._c += 1
        self.__simplify()

    def step_backward(self) :
        if self._c == self.__FIRST_C : return
        num, dom, tmp = (((self._c - 1) % 2) * (-1 if self._c % 4 == 0 else 1)), self._c - 1, self._b
        self._a *= dom
        self._b *= dom
        num *= tmp
        self._a -= num
        self._c -= 1
        self.__simplify()


if __name__ == '__main__' :
    def p_print(p0: Pi) :
        print(f'Step {p0.get_steps()}, Numerator {p0.get_num()} Denominator {p0.get_dom()} = {p0.approximate()} / 4')


    p: Pi = Pi()
    print('Forward')
    for _ in range(30) : p.step_forward()
    p_print(p)
    print('Backward')
    for _ in range(10) : p.step_backward()
    p_print(p)
    print('Forward')
    for _ in range(10) : p.step_forward()
    p_print(p)
    #
    input('Done. ')
    exit()