class_docstr: Common features in univariate interpolation
  
  Deal with input data type and interpolation axis rolling. The
  actual interpolator can assume the y-data is of shape (n, r) where
  `n` is the number of x-points, and `r` the number of variables,
  and use self.dtype as the y-data type.
  
  Attributes
  ----------
  _y_axis
      Axis along which the interpolation goes in the original array
  _y_extra_shape
      Additional trailing shape of the input arrays, excluding
      the interpolation axis.
  dtype
      Dtype of the y-data arrays. Can be set via _set_dtype, which
      forces it to be float or complex.
  
  Methods
  -------
  __call__
  _prepare_x
  _finish_y
  _reshape_yi
  _set_yi
  _set_dtype
  _evaluate
code: def _set_dtype(self, dtype, union=False):
      if np.issubdtype(dtype, np.complexfloating) or np.issubdtype(
          self.dtype, np.complexfloating
      ):
          self.dtype = np.complex_
      else:
          if not union or self.dtype != np.complex_:
              self.dtype = np.float_
  
imports: import numpy
  from scipy.special import factorial
  from scipy._lib._util import _asarray_validated, float_factorial
label_desc: Use image node_id 8 for calling the _Interpolator1D obj's underlying member method code with example usage: obj._set_dtype(dtype, union) without return types