Low level friendly, algebraic solution

def friendly_graded(f, d):
    vec=BoolePolynomialVector()
    for t in f.terms:
        if t.deg()!=d:
            continue
        else:
            vec.append(t)
    return add_up_polynomials(vec)

We leave it to the heuristic of the add_up_polynomials function how to add up the monomials. For example a divide and conquer strategy is quite good here.