How can I create nested item in scrapy?

How can I create a nested item in scrapy like below and yield it:

{"channel": channel, 
     "comid": comid, 
     "siteid": {
             "key1":value1,
             "key2":value2
               }, 
     "url": url, 
     "title":title, 
     "parenturl": parenturl, 
     "tablename": tablename, 
     "fetchtime": fetchtime,
     "images": [ 
         {"imageurl": imageurl,"path": path,"hash":hash},
         {"imageurl": imageurl2,"path": path2,"hash":hash2},
         {........}
     ]
    }