How to load 3D hexahedron mesh file and set the boundaries

[dokken]

@Kepler

import dolfinx

You shouldn’t import dolfinx or use anything from dolfinx in combination with legacy FEniCS. For usage of dolfinx, see:
https://jsdokken.com/dolfinx-tutorial/
and

The new DOLFINx solver is now recommended over DOLFIN

In April 2022 we released versions of the new FEniCS Project components; DOLFINx (v0.4.1) , FFCx (v0.4.2), Basix (v0.4.1) and UFL (2022.1.0.post0). These projects are hosted under our GitHub account at FEniCS Project · GitHub We now recommend that all new projects begin in the new DOLFINx problem solving environment, rather than the old DOLFIN problem solving environment. We consider DOLFINx to be superior to the old DOLFIN, particularly in terms of performance, scalability, API consistency and…