NQuad delete in python – GraphQL

I’m trying to run bulk upsert delete on python as below.

    query = """{
        u as var(func: type(Person))
        }
    """
    #need to use &api.NQuad to delete using Nquad
    nquad = """
        uid(u) * *  .      
    """
    mutation = txn.create_mutation(set_nquads=nquad)
    request = txn.create_request(query=query, mutations=[mutation], commit_now=True)
    txn.do_request(request)

But I get this message
Cannot use star in set n-quad: subject:“uid(u)” predicate:”_STAR_ALL” object_value:<default_val:”_STAR_ALL”

Some documents I found said I need to use &api.nqad, but how can I do that?