code: def get_perplexity_func(perplexity_type):
      func = PERPLEXITY_FUNC_MAP.get(perplexity_type, None)
      if not func:
          raise NotImplementedError
      return func
  
imports: import json
  import math
  import operator
  import time
  import torch
  import torch.nn.functional
  from pytext.common.constants import Stage
  from pytext.config.module_config import PerplexityType
  from pytext.data import CommonMetadata
  from pytext.metrics.language_model_metrics import compute_language_model_metric, LanguageModelMetric
  from pytext.utils import cuda
  from .channel import ConsoleChannel, FileChannel
  from .metric_reporter import MetricReporter
label_desc: Use image node_id 1 for calling a global function with example usage: get_perplexity_func(perplexity_type) and returns: func