How to get constraint node number?

General
1

Dear Sir,
Do you know how to get constraint node number?
For example, I use :
dl.DirichletBC(V_u, dl.Constant((0,1)), boundaries, 2);
to constraint displacement on boundary,
So, do you know how to get node numbers in boundaries-2 ?
Thanks.

2

if by node numbers you mean the index of the DOLFIN.Function you are applying it to, you can either use
bc.get_boundary_values() that gives you a map from the dof number to the value you are applying