code: def _calc_validation_statistics(validation_results):
      
      # calc stats
      successful_expectations = sum(exp["success"] for exp in validation_results)
      evaluated_expectations = len(validation_results)
      unsuccessful_expectations = evaluated_expectations - successful_expectations
      success = successful_expectations == evaluated_expectations
      try:
          success_percent = successful_expectations / evaluated_expectations * 100
      except ZeroDivisionError:
          success_percent = float("nan")
  
      return ValidationStatistics(
          successful_expectations=successful_expectations,
          evaluated_expectations=evaluated_expectations,
          unsuccessful_expectations=unsuccessful_expectations,
          success=success,
          success_percent=success_percent,
      )
docs: Calculate summary statistics for the validation results and
      return ``ExpectationStatistics``.