class_docstr: Calculates metrics for each language given tokenization info.
code: def _format_float_or_none(self, value):
      if isinstance(value, float):
          return "{:.3f}".format(value)
      else:
          return None
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import collections
  import apache_beam
  import tensorflow.compat.v1
  from tensorflow_text.python.ops.bert_tokenizer import BertTokenizer
  from tensorflow_text.python.ops.wordpiece_tokenizer import WordpieceTokenizer
  from tensorflow_text.tools.wordpiece_vocab import wordpiece_tokenizer_learner_lib
label_desc: Use image node_id 8 for calling the CalculateMetrics obj's underlying member method code with example usage: obj._format_float_or_none(value) and returns: str, None