mesh.faces.delete(1, range(0, len(mesh.faces)))
for i,f in enumerate(nmesh.faces):
fv = [v.index for v in f.v]
mesh.faces.extend(fv)
mesh.faces[i].mat = f.mat
mesh.faces.delete(1, range(0, len(mesh.faces)))
for i,f in enumerate(nmesh.faces):
fv = [v.index for v in f.v]
mesh.faces.extend(fv)
mesh.faces[i].mat = f.mat