code: def test_loc_setitem_single_column_slice():
      # case from https://github.com/pandas-dev/pandas/issues/27841
      df = DataFrame(
          "string",
          index=list("abcd"),
          columns=MultiIndex.from_product(
              [["Main"], ("another", "one")]
          ),
      )
      df["labels"] = "a"
      df.loc[:, "labels"] = df.index
      tm.assert_numpy_array_equal(
          np.asarray(df["labels"]), np.asarray(df.index)
      )
  
      # test with non-object block
      df = DataFrame(
          np.nan,
          index=range(4),
          columns=MultiIndex.from_tuples(
              [("A", "1"), ("A", "2"), ("B", "1")]
          ),
      )
      expected = df.copy()
      df.loc[:, "B"] = np.arange(4)
      expected.iloc[:, 2] = np.arange(4)
      tm.assert_frame_equal(df, expected)
  
imports: import numpy
  import pytest
  from pandas.errors import IndexingError, PerformanceWarning
  import pandas
  from pandas import DataFrame, Index, MultiIndex, Series
  import pandas._testing
label_desc: Use image node_id 9 for calling a global function with example usage: test_loc_setitem_single_column_slice() without return types