class_docstr: S3Rec is the first work to incorporate self-supervised learning in
  sequential recommendation.
  
  NOTE:
      Under this framework, we need reconstruct the pretraining data,
      which would affect the pre-training speed.
code: def _padding_zero_at_left(self, sequence):
      # had truncated according to the max_length
      pad_len = self.max_seq_length - len(sequence)
      sequence = [0] * pad_len + sequence
      return sequence
  
imports: import random
  import torch
  from torch import nn
  from recbole.model.abstract_recommender import SequentialRecommender
  from recbole.model.layers import TransformerEncoder
  from recbole.model.loss import BPRLoss
label_desc: Use image node_id 10 for calling the S3Rec obj's underlying member method code with example usage: obj._padding_zero_at_left(sequence) and returns: sequence