code: def testStd(self):
      # Defined for all batch members.
      df = [3.5, 5.0, 3.0, 5.0, 7.0]
      loc = [-2.2]
      sigma = [5.0, 4.0, 3.0, 2.0, 1.0]
      half_student = half_student_t.HalfStudentT(
          df=df, loc=loc, scale=sigma, validate_args=True
      )
      # Test broadcast of loc across shape of df/sigma
      stddev = self.evaluate(half_student.stddev())
      loc *= len(df)
  
      expected_var = _true_variance(df, sigma)
      self.assertAllClose(expected_var**0.5, stddev)
  
imports: import math
  import numpy
  from scipy import stats
  from scipy.special import gamma
  import tensorflow.compat.v2
  from tensorflow_probability.python.distributions import half_student_t
  from tensorflow_probability.python.distributions.internal import statistical_testing
  from tensorflow_probability.python.internal import assert_util
  from tensorflow_probability.python.internal import test_util
  from tensorflow_probability.python.math import gradient
label_desc: Use image node_id 18 for calling the HalfStudentTTest obj's underlying member method code with example usage: obj.testStd() without return types