code: def test_single_element_std() -> None:
      s = pl.Series([1])
      assert s.std(ddof=1) is None
      assert s.std(ddof=0) == 0.0
  
imports: from __future__ import annotations
  from datetime import date, datetime, timedelta
  from typing import TYPE_CHECKING, Any
  import numpy
  import pytest
  import polars
  from polars.testing import assert_frame_equal
label_desc: Use image node_id 7 for calling a global function with example usage: test_single_element_std() without return types