code: def df() -> pl.DataFrame:
      return pl.DataFrame(
          {
              "a": [1, 2, 3, 4, 5],
              "b": ["a", "a", "b", "b", "b"],
              "c": [None, 1, None, 1, None],
          }
      )
  
imports: from __future__ import annotations
  from collections import OrderedDict
  from datetime import datetime, timedelta
  from typing import Any
  import pytest
  import polars
  from polars.testing import assert_frame_equal, assert_series_equal
label_desc: Use image node_id 2 for calling a global function with example usage: df() and returns: pl