input: Write a function to create a Car object in Python with attributes for make, model, color, and mileage, and methods to accelerate and decelerate the car. Return the Car object.
  assert create_car("Toyota", "Camry", "Red", 5000).__dict__=={'make': 'Toyota', 'model': 'Camry', 'color': 'Red', 'mileage': 5000, 'speed': None}
  assert create_car("Honda", "Civic", "Blue", 10000).accelerate(60).speed==60
  assert create_car("Ford", "Mustang", "Black", 8000).decelerate(30).speed==30
  assert create_car("Chevrolet", "Cruze", "White", 15000).__dict__=={'make': 'Chevrolet', 'model': 'Cruze', 'color': 'White', 'mileage': 15000, 'speed': None}
output: def create_car(make, model, color, mileage):
      class Car:
          def __init__(self, make, model, color, mileage):
              self.make = make
              self.model = model
              self.color = color
              self.mileage = mileage
              self.speed = None
          
          def accelerate(self, speed):
              self.speed = speed
              return self
          
          def decelerate(self, speed):
              self.speed = speed
              return self
      
      return Car(make, model, color, mileage)