code: def great_circle_distance(pt1, pt2):
      
      r = 6371.
  
      delta_latitude = math.radians(pt1[0] - pt2[0])
      delta_longitude = math.radians(pt1[1] - pt2[1])
      latitude1 = math.radians(pt1[0])
      latitude2 = math.radians(pt2[0])
  
      a = math.sin(delta_latitude / 2) ** 2 + math.cos(latitude1) * math.cos(latitude2) * math.sin(delta_longitude / 2) ** 2
      return r * 2. * math.asin(math.sqrt(a))
docs: Return the great-circle distance in kilometers between two points,
      defined by a tuple (lat, lon).
  
      Examples
      --------
      >>> brussels = (50.8503, 4.3517)
      >>> paris = (48.8566, 2.3522)
      >>> great_circle_distance(brussels, paris)
      263.9754164080347