修改无效
nodes = pd.read_csv("pre_only_num.csv",header =None)
for index,row in nodes.iterrows():
    #print(row[0])
    row[0] = -1

直接在原处修改无效

        for index,row in nodes.iterrows():
            oid = int(row[0])
            
            nodes.iat[index,0] = self.idmap[oid]# !!!