old_contents: 
  from astropy.io import fits
  import numpy as np
  
  from ..io import input_data
  
  
  class BaseStatisticMixIn(object):
      """
      Common properties to all statistics
      """
  
      # Disable this flag when a statistic does not need a header
      need_header_flag = True
  
      @property
      def header(self):
          return self._header
  
      @header.setter
      def header(self, input_hdr):
  
          if not self.need_header_flag:
              input_hdr = None
  
          elif not isinstance(input_hdr, fits.header.Header):
              raise TypeError("The header must be a"
                              " astropy.io.fits.header.Header.")
  
          self._header = input_hdr
  
      @property
      def data(self):
          return self._data
  
      @data.setter
      def data(self, values):
  
          if not isinstance(values, np.ndarray):
              raise TypeError("Data is not a numpy array.")
  
          self._data = values
  
      def input_data_header(self, data, header):
          '''
          Check if the header is given separately from the data type.
          '''
  
          if header is not None:
              self.data = input_data(data, no_header=True)
              self.header = header
          else:
              self.data, self.header = input_data(data)
  
new_contents: 
  from astropy.io import fits
  import numpy as np
  
  from ..io import input_data
  
  
  class BaseStatisticMixIn(object):
      """
      Common properties to all statistics
      """
  
      # Disable this flag when a statistic does not need a header
      need_header_flag = True
  
      # Disable this when the data property will not be used.
      no_data_flag = False
  
      @property
      def header(self):
          return self._header
  
      @header.setter
      def header(self, input_hdr):
  
          if not self.need_header_flag:
              input_hdr = None
  
          elif not isinstance(input_hdr, fits.header.Header):
              raise TypeError("The header must be a"
                              " astropy.io.fits.header.Header.")
  
          self._header = input_hdr
  
      @property
      def data(self):
          return self._data
  
      @data.setter
      def data(self, values):
  
          if self.no_data_flag:
              values = None
  
          elif not isinstance(values, np.ndarray):
              raise TypeError("Data is not a numpy array.")
  
          self._data = values
  
      def input_data_header(self, data, header):
          '''
          Check if the header is given separately from the data type.
          '''
  
          if header is not None:
              self.data = input_data(data, no_header=True)
              self.header = header
          else:
              self.data, self.header = input_data(data)
  
subject: Allow data property to not be use