input: 
  class MedianFinder:
      def __init__(self):
          self._data = []
      
      def add(self, num):
          self._data.append(num)
      
      def find_median(self):
          data = sorted(self._data)
          n = len(data)
          return (data[(n-1)//2] + data[n//2])/2
  
  """
  A class that allows you to add numbers to a list and then find the median of the list.
  >>> finder = MedianFinder()
  >>> finder.add(1)
  >>> finder.add(2)
  >>> finder.add(3)
  >>> finder.find_median()
  2.0
  >>> finder.add(4)
  >>> finder.find_median()
  2.5
  """
  
output:     
      def __repr__(self):
          return f"MedianFinder(data={self._data})"
  