class Y:
    def __init__(self, v0):
        self.v0 = v0
        self.g = 9.81

    def __call__(self, t):
        return self.v0*t - 0.5*self.g*t**2

    def __str__(self):
        return f'v0*t -0.5*g*t**2, v0 = {self.v0}'


    def __repr__(self):
        return f'Y({self.v0})'


y = Y(v0=5)
print(y(2))
y2 = eval((repr(y)))

print(y2)