input: 
  class MedianFinder:
      """
      A class that allows the finding of the median in an unsorted list of numbers.
      
      >>> mf = MedianFinder()
      >>> mf.add(1)
      >>> mf.add(3)
      >>> mf.add(2)
      >>> mf.find_median()
      2.0
      >>> mf.add(4)
      >>> mf.find_median()
      2.5
      """
      def __init__(self):
          """ Initialize an empty list to store numbers. """
          self._data = []
  
      def add(self, num):
          """ Add a number to the list. """
          self._data.append(num)
  
      def find_median(self):
          """ Return the median of the list of numbers. """
          data = sorted(self._data)
          n = len(data)
          return (data[(n-1)//2] + data[n//2]) / 2
  
output:     
      def __init__(self):
          """ Initialize an empty list to store numbers. """
          self._data = []
  
      def add(self, num):
          """ Add a number to the list. """
          self._data.append(num)
  
      def find_median(self):
          """ Return the median of the list of numbers. """
          data = sorted(self._data)
          n = len(data)
          return (data[(n-1)//2] + data[n//2]) / 2
  