Merge Meshes

[reox]

I just wanted to use meshio to write me nice vtk files for some meshes, and therefore I need to merge multiple meshes together.
I did not found a direct way to do that, thus I wrote this (very simplified and not generally usable) function:

import meshio

def merge_meshes(a: meshio.Mesh = None, b: meshio.Mesh = None) -> meshio.Mesh:
    if a is None:
        return b
    if b is None:
        return a
    n_vert = a.points.shape[0]
    vertices = np.vstack((a.points, b.points))
    all_cell_types = a.cells_dict.keys() & b.cells_dict.keys()
    cells = dict()
    for cell_type in all_cell_types:
        if cell_type in a.cells_dict and cell_type in b.cells_dict:
            cells[cell_type] = np.vstack((a.cells_dict[cell_type], b.cells_dict[cell_type] + n_vert))
        elif cell_type in a.cells_dict:
            cells[cell_type] = a.cells_dict[cell_type]
        elif cell_type in b.cells_dict:
            cells[cell_type] = b.cells_dict[cell_type] + n_vert
    return meshio.Mesh(vertices, cells)

It simply concatenates the point vectors and adjusts the numbering in the second mesh.
Because that could be useful for other things as well, I wondered, if I overlooked something and there is more generic way already implemented?