class_docstr: Mask item sequence for training.
class_docstr_tok: ["Mask","item","sequence","for","training","."]
code: def _neg_sample(self, item_set, n_items):
      item = random.randint(1, n_items - 1)
      while item in item_set:
          item = random.randint(1, n_items - 1)
      return item
  
imports: import math
  import numpy
  import random
  import torch
  from copy import deepcopy
  from recbole.data.interaction import Interaction, cat_interactions
label_desc: Use image node_id 2 for calling the MaskItemSequence obj's underlying member method code with example usage: obj._neg_sample(item_set, n_items) and returns: item