code: def __repr__(self):
      return "GPT2Perplexity"
  
file_path: textflint/textflint/generation/validator/gpt2_perplexity.py
imports: import math
  import torch
  from transformers import GPT2Tokenizer, GPT2LMHeadModel
  from .validator import Validator
label_desc: Use image node_id 2 for calling the GPT2Perplexity obj's underlying member method code with example usage: obj.__repr__() and returns: str