code: def effective_dtype(self, dtype):
      if dtype is None:
          return np.uint8
      return dtype
  
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 4 for calling the TestGetDummies obj's underlying member method code with example usage: obj.effective_dtype(dtype) and returns: dtype, np