input: 
  from typing import List
  
  class MedianFinder:
      """This class can find the median of an unsorted list of numbers.
      Example usage:
      finder = MedianFinder()
      finder.add(1)
      finder.add(2)
      finder.add(3)
      assert finder.find_median() == 2.0
      finder.add(4)
      assert finder.find_median() == 2.5
      """
      
      def __init__(self):
          self._data = []
      
      def add(self, num: float) -> None:
          self._data.append(num)
      
      def find_median(self) -> float:
          data = sorted(self._data)
          n = len(data)
          return (data[(n-1)//2] + data[n//2])/2
  
output:     
      def __init__(self):
          self._data = []
      
      def add(self, num: float) -> None:
          self._data.append(num)
      
      def find_median(self) -> float:
          data = sorted(self._data)
          n = len(data)
          return (data[(n-1)//2] + data[n//2])/2
  