input: Write a function to find the closest pair of points from a list using Euclidean distance.
  assert closest_pair([(1, 2), (3, 4), (6, 8), (7, 7)])==((6, 8), (7, 7))
  assert closest_pair([(0, 0), (5, 5), (9, 9), (2, 3)])==((0, 0), (2, 3))
  assert closest_pair([(1, 1), (2, 2), (3, 3), (1.5, 1.5)])==((1, 1), (1.5, 1.5))
output: def closest_pair(points):
      import math
      min_distance = float('inf')
      closest_pair = None
      
      def euclidean_distance(p1, p2):
          return math.sqrt((p1[0] - p2[0]) ** 2 + (p1[1] - p2[1]) ** 2)
      
      for i in range(len(points)):
          for j in range(i + 1, len(points)):
              dist = euclidean_distance(points[i], points[j])
              if dist < min_distance:
                  min_distance = dist
                  closest_pair = (points[i], points[j])
      
      return closest_pair