code: def __len__(self):
      return len(self.members)
  
imports: from __future__ import print_function
  import random
  import csv
  import operator
  import gc
  import os
  from datetime import datetime
  from keras.callbacks import EarlyStopping
  from keras.models import load_model
  import keras.backend
  from sklearn.metrics import log_loss
  import numpy
label_desc: Use image node_id 1 for calling the _Population obj's underlying member method code with example usage: obj.__len__() and returns: len