input: Write a python function to create a Circle class, calculate its area and circumference, and represent it as a string.
  assert str(Circle(5)) == 'Circle at (0, 0) with radius 5'
  assert Circle(5).area() == 25 * math.pi
  assert Circle(5).circumference() == 10 * math.pi
  assert str(Circle(10, 3, 4)) == 'Circle at (3, 4) with radius 10'
  assert Circle(10, 3, 4).area() == 100 * math.pi
  assert Circle(10, 3, 4).circumference() == 20 * math.pi
output: import math
  
  class Circle:
      def __init__(self, radius, x=0, y=0):
          self.radius = radius
          self.x = x
          self.y = y
  
      def area(self):
          return math.pi * self.radius ** 2
  
      def circumference(self):
          return 2 * math.pi * self.radius
  
      def __str__(self):
          return f'Circle at ({self.x}, {self.y}) with radius {self.radius}'