MAINT: update Atom.xyz, _U arrays in place.

Use consistent in-place array assignment regardless
of unset lattice or anisotropy.

Author: pavoljuhas

src/diffpy/Structure/atom.py

@@ -193,7 +193,7 @@ def _set_xyz_cartn(self, value):
         if not self.lattice:
             self.xyz[:] = value
         else:
-            self.xyz = self.lattice.fractional(value)
+            self.xyz[:] = self.lattice.fractional(value)
         return
 
     xyz_cartn = property(_get_xyz_cartn, _set_xyz_cartn, doc =
@@ -227,7 +227,7 @@ def _get_U(self):
             # for isotropic displacements assume first element
             # to be equal to the displacement value
             lat = self.lattice or cartesian_lattice
-            self._U = self._U[0, 0] * lat.isotropicunit
+            numpy.multiply(self._U[0, 0], lat.isotropicunit, out=self._U)
         return self._U
 
     def _set_U(self, value):