code: def cross_sampling(self):
      self.cross_sampling_flag = 1 - self.cross_sampling_flag
      if self.cross_sampling_flag == 0:
          return self.sampling_head()
      else:
          return self.sampling_tail()
  
imports: import os
  import ctypes
  import numpy
label_desc: Use image node_id 6 for calling the TrainDataLoader obj's underlying member method code with example usage: obj.cross_sampling() and returns: self, self