How to assign empty argument in Class to integer 0?

Question

class Car:
   def __init__(self, model, year, speed):
     self.model = model
     self.year = year
     self.speed = speed
    
   def strModel(self):
     return str(self.model)

   def accelerate(self):
     accelerate = 5
     self.speed = self.speed + accelerate

   def brake(self):
     brake = 5
     self.speed = self.speed - brake
    

     my_car = Car("Tesla", 2020)
     my_car.accelerate()
     my_car.accelerate()
     my_car.brake()
     print(my_car.speed)

So if I change the class arguments to ("Tesla", 2020, 30) I will get the correct answer which is 35. But what I want to do is even though I didn't assign an argument for speed like above, it will automatically assign to 0 so the answer should be 5.