code: def test_dataframe_dummies_prefix_sep(self, df, sparse):
      result = get_dummies(df, prefix_sep="..", sparse=sparse)
      expected = DataFrame(
          {
              "C": [1, 2, 3],
              "A..a": [True, False, True],
              "A..b": [False, True, False],
              "B..b": [True, True, False],
              "B..c": [False, False, True],
          },
      )
      expected[["C"]] = df[["C"]]
      expected = expected[["C", "A..a", "A..b", "B..b", "B..c"]]
      if sparse:
          cols = ["A..a", "A..b", "B..b", "B..c"]
          expected[cols] = expected[cols].astype(
              SparseDtype("bool", False)
          )
  
      tm.assert_frame_equal(result, expected)
  
      result = get_dummies(df, prefix_sep=["..", "__"], sparse=sparse)
      expected = expected.rename(
          columns={"B..b": "B__b", "B..c": "B__c"}
      )
      tm.assert_frame_equal(result, expected)
  
      result = get_dummies(
          df, prefix_sep={"A": "..", "B": "__"}, sparse=sparse
      )
      tm.assert_frame_equal(result, expected)
  
imports: import re
  import unicodedata
  import numpy
  import pytest
  import pandas.util._test_decorators
  from pandas.core.dtypes.common import is_integer_dtype
  import pandas
  from pandas import ArrowDtype, Categorical, CategoricalDtype, CategoricalIndex, DataFrame, Index, RangeIndex, Series, SparseDtype, get_dummies
  import pandas._testing
  from pandas.core.arrays.sparse import SparseArray
label_desc: Use image node_id 17 for calling the TestGetDummies obj's underlying member method code with example usage: obj.test_dataframe_dummies_prefix_sep(df, sparse) without return types