human
I wrote the below code

    domains = [chr((ord('a') + i)) for i in range(13)]
    L = [resolver.getHostByName(('%s.root-servers.net' % d)) for d in domains]
    d = defer.DeferredList(L)
    def buildResolver(res):
        return Resolver(hints=[e[1] for e in res if e[0]], resolverFactory=resolverFactory)
    d.addCallback(buildResolver)
    return DeferredResolver(d)

What's a good function header?
assistant
#Here's a good function header.

def bootstrap(resolver, resolverFactory=None):