code: def _calc_expected_predictions_length(self, predict_input, top_k=1):
      input_sessions = predict_input.groupby(
          self.session_id, {"session_len": tc.aggregate.COUNT()}
      )
      prediction_window = self.model.prediction_window
      input_sessions["num_predictions_per_session"] = input_sessions[
          "session_len"
      ].apply(lambda x: math.ceil(float(x) / prediction_window))
      total_num_of_prediction = (
          sum(input_sessions["num_predictions_per_session"]) * top_k
      )
  
      return total_num_of_prediction
  
imports: from __future__ import print_function
  from __future__ import division
  from __future__ import absolute_import
  import unittest
  import turicreate
  import random
  import tempfile
  import math
  import numpy
  from numbers import Number
  from .None import util
  import pytest
  from turicreate.toolkits._internal_utils import _mac_ver
  from turicreate.toolkits._main import ToolkitError
  import uuid
label_desc: Use image node_id 2 for calling the ActivityClassifierTest obj's underlying member method code with example usage: obj._calc_expected_predictions_length(predict_input, top_k) and returns: total_num_of_prediction