new_contents: #! /usr/bin/env python3
  # -*- coding: utf-8 -*-
  
  class Hemidataset:
      def __init__(self):
          self.surfs = {}
  
          # Init the dataset, not sure if it's proper
          self.surflist = ['white', 'pial', 'inflated', 'flated']
          for i in self.surflist:
              self.surfs.update({i: ''})
  
      def add_surface(self, type, surf_path, offset=None):
          '''Add surface data into the surfs'''
          if self.insurflist(type):
              self.surfs[type] = [surf_path, offset]
  
      def insurflist(self, type):
          '''To judge if the type is in the surflist.'''
          list = self.get_surflist()
          for item in list:
              if type == item:
                  return True
          return False
  
      def get_surflist(self):
          '''To get the surflist.'''
          return self.surflist
  
      '''Another way to add surface data, respectively.'''
      def add_whitesurface(self, surf_path, offset=None):
          self.surfs['white'] = [surf_path, offset]
  
      def add_pialsurface(self, surf_path, offset=None):
          self.surfs['pial'] = [surf_path, offset]
  
      def add_inflatedsurface(self, surf_path, offset=None):
          self.surfs['inflated'] = [surf_path, offset]
  
      def add_flatedsurface(self, surf_path, offset=None):
          self.surfs['flated'] = [surf_path, offset]
  
      def get_surfs(self):
          '''Just for test.'''
          return self.surfs
  
  if __name__ == '__main__':
      instance1 = Hemidataset()
      # The first method for adding.
      instance1.add_surface('white', 'path_white', 123)
      instance1.add_surface('pial', 'path_pial', 'small')
      # The second method.
      instance1.add_inflatedsurface('path_inflated')
      instance1.add_flatedsurface('path_flated')
      print(instance1.get_surfs())
      # The print result is:
      # {'white': ['path_white', 123], 'inflated': ['path_inflated', None], 'flated': ['path_flated', None], 'pial': ['path_pial', 'small']}
  
subject: add surface dataset