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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _preprocess(self, x, out=None):
 """Return the pre-processed version of ``x``. C2C: use ``tmp_r`` or ``tmp_f`` (C2C operation) R2C: use ``tmp_f`` (R2C operation) HALFC: use ``tmp_r`` (R2R operation) The result is stored in ``out`` if given, otherwise in a temporary or a new array. """

        if out is None:
            if self.domain.field == ComplexNumbers():
                out = self._tmp_r if self._tmp_r is not None else self._tmp_f
            elif self.domain.field == RealNumbers() and not self.halfcomplex:
                out = self._tmp_f
            else:
                out = self._tmp_r
        return dft_preprocess_data(
            x, shift=self.shifts, axes=self.axes, sign=self.sign,
            out=out)