code: def _call(self, x):
          
          if self.impl == 'pywt':
              coeffs = pywt.wavedecn(
                  x, wavelet=self.pywt_wavelet, level=self.nlevels,
                  mode=self.pywt_pad_mode, axes=self.axes)
              return pywt.ravel_coeffs(coeffs, axes=self.axes)[0]
          else:
              raise RuntimeError("bad `impl` '{}'".format(self.impl))
docs: Return wavelet transform of ``x``.