from petsc4py import PETSc

cells = [[0, 1, 2], [1, 3, 2]]
coords = [[0., 0.], [1., 0], [0., 1.], [1., 1.]]
plex = PETSc.DMPlex().createFromCellList(2, cells, coords)
plex.setName('square')

viewer = PETSc.ViewerHDF5().create(
    'square.h5', mode=PETSc.Viewer.Mode.WRITE, comm=PETSc.COMM_WORLD
)

viewer.pushGroup('/meshes')
print(viewer.getGroup())
plex.view(viewer)
viewer.popGroup()