input: Write a function to create a class in Python to store and process data in a Car object. The class should have an initializer to store attributes like make, model, color, and mileage. It should also have methods to accelerate and decelerate the car by a given speed.
  class Car:
      def __init__(self, make, model, color, mileage):
          self.make = make
          self.model = model
          self.color = color
          self.mileage = mileage
  
      def accelerate(self, speed):
          self.speed = speed
  
      def decelerate(self, speed):
          self.speed = speed
  
  assert Car("Toyota", "Corolla", "Red", 50000).make == "Toyota"
  assert Car("Honda", "Civic", "Blue", 30000).model == "Civic"
  assert Car("Ford", "Mustang", "Black", 20000).color == "Black"
  assert Car("Tesla", "Model S", "White", 10000).mileage == 10000
  assert Car("BMW", "X5", "Silver", 40000).accelerate(60) == None
  assert Car("Audi", "A4", "Gray", 60000).decelerate(20) == None
output: def __init__(self, make, model, color, mileage):
      self.make = make
      self.model = model
      self.color = color
      self.mileage = mileage
      self.speed = 0
  
  def accelerate(self, speed):
      self.speed += speed
  
  def decelerate(self, speed):
      self.speed -= speed