code: def calculate_loss(self) -> float:
      if self.total_num_tokens == 0:
          return 0.0
      return self.aggregate_loss / float(self.total_num_tokens)
  
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 4 for calling the LanguageModelMetricReporter obj's underlying member method code with example usage: obj.calculate_loss() and returns: unknown, int