code: def test_series_std(ddof):
      np.random.seed(0)
      arr = np.random.random(100) - 0.5
      sr = cudf.Series(arr)
      pd = sr.to_pandas()
      got = sr.std(ddof=ddof)
      expect = pd.std(ddof=ddof)
      np.testing.assert_approx_equal(expect, got)
  
imports: from concurrent.futures import ThreadPoolExecutor
  import cupy
  import numpy
  import pandas
  import pytest
  import cudf
  from cudf.datasets import randomdata
  from cudf.testing._utils import _create_cudf_series_float64_default, _create_pandas_series_float64_default, assert_eq, assert_exceptions_equal, expect_warning_if
label_desc: Use image node_id 3 for calling a global function with example usage: test_series_std(ddof) without return types