code: def isnan(x: Any) -> bool:
      return isinstance(x, float) and math.isnan(x)
  
imports: from __future__ import annotations
  import math
  from contextlib import nullcontext
  from typing import Any, ContextManager
  import pytest
  import polars
  from polars.testing import assert_frame_equal
label_desc: Use image node_id 8 for calling a global function with example usage: isnan(x) and returns: unknown