docs: def makeRetweetNetwork(tweets):
      """Receives tweets, returns directed retweet networks.
      
      Without and with isolated nodes.
      """
      G=x.DiGraph()
      G_=x.DiGraph()
      for tweet in tweets:
          text=tweet["text"]
          us=tweet["user"]["screen_name"]
          if text.startswith("RT @"):
              prev_us=text.split(":")[0].split("@")[1]
              #print(us,prev_us,text)
              if G.has_edge(prev_us,us):
                  G[prev_us][us]["weight"]+=1
                  G_[prev_us][us]["weight"]+=1
              else:
                  G.add_edge(prev_us, us, weight=1.)
                  G_.add_edge(prev_us, us, weight=1.)
          if us not in G_.nodes():
              G_.add_node(us)
      return G,G_