为什么我不能在列表中的对象上调用 __dict__ ，而该对象恰好在字典中的列表中的另一个对象中？

Question

Here's my setup: dictD contains a key users paired with value = list of UserObjects . Each UserObject has an attribute username plus two arrays, threads and comments.

I was able to convert dictD's array of user objects into a dictionary style with this call:

dictD["users"] = [user.__dict__ for user in dictD["users"] ]

If I dump out dictD, here's the relevant part before I try to do my manipulation:

{
    'users':[
    {
        'username': Redditor(user_name='$$$$$$$$$$'),
        'threads':[
            <__main__.redditThread instance at 0x7f05db28b320>
        ],
    'comments':[
        <__main__.comment instance at 0x7f05db278e60>
    ]
},
{
    'username': Redditor(user_name='##########e\ gone'),
    'threads':[
        <__main__.redditThread instance at 0x7f05db2a4a70>
    ],
    'comments':[
        <__main__.comment instance at 0x7f05db298e18>
    ]
}

As you can see the comments contain comment objects and the threads list contains thread objects. So I'd like to do the same call for them that I did for the users array. But when I try to do this:

for user in dictD["users"]:
    user.threads = [thread.__dict__ for thread in user.threads]
    user.comments = [comment.__dict__ for comment in user.comments]

I run into this error:

AttributeError: 'dict' object has no attribute 'threads'

I also tried

users = dictD["users"]
for user in users...

but this triggers the same error message. How can I turn objects in lists into dictionary form when those objects' lists are themselves held within objects within lists within a dictionary?

Incidentally, I am doing all this so I can insert these objects into MongoDB, so if there is an easier way to serialize a complex object, please let me into the secret. Thank you.

Answer 1

Promoting my comment to an answer since it seems reasonable and nobody else is posting: it looks at a glance like you're confusing Python for Javascript: a dict with a key 'threads' is not an object you can reference with .threads , only with ["threads"] . ie. user.threads should be user["threads"] . A dict usually only has the same standard attributes (see: https://docs.python.org/2/library/stdtypes.html#typesmapping or https://docs.python.org/3/library/stdtypes.html#mapping-types-dict for Python 3.) The problem isn't that you're trying to call __dict__ on an object, it's that you're trying to get an attribute from an object that doesn't exist, later in that same line of code.

If you want to recreate complex objects from MongoDB rather than just nested dicts and lists then that is basically a process of deserialization; you can either handle that manually, or maybe use some sort of object mapping library to do it for you (eg. something like Mongoobject might work, though I've not tested it myself)