input: Write a python function to calculate the area and circumference of a circle given its radius.
  assert Circle(5).area() == 78.5
  assert Circle(5).circumference() == 31.400000000000002
  assert Circle(10).area() == 314.0
  assert Circle(10).circumference() == 62.800000000000004
output: import math
  
  class Circle:
      def __init__(self, radius):
          self.radius = radius
  
      def area(self):
          return math.pi * self.radius ** 2
  
      def circumference(self):
          return 2 * math.pi * self.radius