code: def test_std(self):
      d = fo.Dataset()
      d.add_sample_field("numeric_field", fo.IntField)
      self.assertEqual(d.std("numeric_field"), 0)
  
      s = fo.Sample(filepath="image.jpeg", numeric_field=1)
      d.add_sample(s)
      self.assertEqual(d.std("numeric_field"), 0)
  
      s = fo.Sample(filepath="image2.jpeg", numeric_field=3)
      d.add_sample(s)
      self.assertEqual(d.std("numeric_field"), 1)
  
      self.assertAlmostEqual(d.std(2.0 * (F("numeric_field") + 1)), 2.0)
  
imports: from datetime import date, datetime, timedelta
  import math
  from bson import ObjectId
  import numpy
  import unittest
  import fiftyone
  import fiftyone.core.fields
  from fiftyone import ViewField
  from decorators import drop_datasets
label_desc: Use image node_id 10 for calling the DatasetTests obj's underlying member method code with example usage: obj.test_std() without return types