input: from typing import List
  
  
  class MedianFinder:
      """A class that can find the median of an unsorted list of numbers.
      >>> finder = MedianFinder()
      >>> finder.add(3)
      >>> finder.add(1)
      >>> finder.add(2)
      >>> finder.find_median()
      2.0
      >>> finder.add(4)
      >>> finder.find_median()
      2.5
      """
      
      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
output:     
      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
  