code: def test_columns_generic_hashable():
      """Checks flag_nulls behaviour when columns is a generic hashable."""
      df = pd.DataFrame(
          {
              25: ["w", "x", None, "z"],
              ("weird", "col"): [5, None, 7, 8],
              "normal": [1, 2, 3, 4],
          }
      )
      expected = df.copy().assign(null_flag=[0, 0, 1, 0])
  
      df = df.flag_nulls(columns=25)
      assert_frame_equal(df, expected, check_dtype=False)
  
file_path: pyjanitor/tests/functions/test_flag_nulls.py
imports: import pandas
  import pytest
  from pandas.testing import assert_frame_equal
  from janitor.functions import flag_nulls
label_desc: Use image node_id 4 for calling a global function with example usage: test_columns_generic_hashable() without return types