code: def _np_hann_periodic_window(length):
      if length == 1:
          return np.ones(1)
      odd = length % 2
      if not odd:
          length += 1
      window = 0.5 - 0.5 * np.cos(
          2.0 * np.pi * np.arange(length) / (length - 1)
      )
      if not odd:
          window = window[:-1]
      return window
  
imports: import itertools
  from absl.testing import parameterized
  import numpy
  from tensorflow.python.eager import context
  from tensorflow.python.framework import dtypes
  from tensorflow.python.framework import test_util
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import gradient_checker_v2
  from tensorflow.python.ops import gradients_impl
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops.signal import spectral_ops
  from tensorflow.python.ops.signal import window_ops
  from tensorflow.python.platform import test
label_desc: Use image node_id 1 for calling the SpectralOpsTest obj's underlying member method code with example usage: obj._np_hann_periodic_window(length) and returns: window, np