How can I specify order of data in Attrs?-CodePudding

Taking from attrs example here but adding group_id. I want to create data classes so I can then export them to JSON using json.dump().

@define
class User:
    email: str
    password: str

@define
class UserList:
    users: list[User]
    group_id: str = field(default=str(uuid4()), on_setattr=frozen)

json.dump(asdict(UserList([User("[email protected]", "s33kred"),
                 User("[email protected]", "p4ssw0rd")]),
       filter=lambda attr, value: attr.name != "password"))

That prints out this:

{"users": [{"email": "[email protected]"}, {"email": "[email protected]"}], "group-id": "a9fc0c10-125f-4c65-a901-ac16e3b57bc7"}

However, my issue is that I want group-id to be at the very top, like this:

{"group-id": "a9fc0c10-125f-4c65-a901-ac16e3b57bc7", "users": [{"email": "[email protected]"}, {"email": "[email protected]"}]}

It seems that attrs organise them on initialisation and because group-id has a default value, I am unable to place it at the top.

Any thoughts on how to solve this issue?

CodePudding user response：

Which Python version? As of Python 3.7 dictionaries are insertion ordered so asdict should respect the order of the fields as you provided them.

You could also change the dict_factory arg of attr.asdict to use collections.OrderedDict to enforce this otherwise.

CodePudding user response：

Do you want to sort your keys in the end? You can do it by passing sort_keys=True. For example:

import json
print(
    json.dumps(
        {"users": [
            {"email": "[email protected]"},
            {"email": "[email protected]"}
        ],
            "group-id": "a9fc0c10-125f-4c65-a901-ac16e3b57bc7"},
        sort_keys=True
    )
)

Output:

{"group-id": "a9fc0c10-125f-4c65-a901-ac16e3b57bc7", "users": [{"email": "[email protected]"}, {"email": "[email protected]"}]}