input: 
  class MedianFinder:
      """A class to find the median of an unsorted list of numbers.
      The class has methods to add numbers and find the median.
      
      >>> mf = MedianFinder()
      >>> mf.add(3)
      >>> mf.add(1)
      >>> mf.add(2)
      >>> mf.find_median()
      2.0
      >>> mf.add(4)
      >>> mf.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
  