Deserializing datetime double encodes date - django

Question

I am trying to deserialize a datetime value:
def default(o):
if type(o) is datetime.date or type(o) is datetime.datetime:
return o.isoformat()
def get_user_join_date(user):
return json.dumps(
user.date_joined,
sort_keys=True,
indent=1,
default=default
)
in order to use it as a value in payload:
def jwt_payload_handler(user, active_site):
payload = {
"id": user.id,
"date": get_user_join_date(user),
"username": user.username,
"role": user.role
}
The problem is that my datetime ends up being double encoded (it has 2 double quotes)
date: ""2018-09-27T12:32:17.577000+00:00""
Any idea why this might be happening and how I can solve it?

Answer 1

What's happening here is that the date string is encoded twice.
The return value of get_user_join_date(user) is the string '"2018-09-27T12:32:17.577000+00:00"' (so the ISO formatted datetime surrounded by double quotes).
This string is put into the payload and is again dumped to JSON by whatever you're using to create the JWT token.
A reduced example of what you are seeing would be this:
import json
import datetime
def default(o):
if type(o) is datetime.date or type(o) is datetime.datetime:
return o.isoformat()
print(json.dumps({
'date': json.dumps(
datetime.datetime.now(),
default=default
)
}))
Which produces the output you are seeing:
{"date": "\"2018-10-09T12:53:04.914694\""}
There are a few solutions to this issue:
The easiest solution to this issue would be to not use json.dumps in get_user_join_date and simply return user.date_joined.isoformat() instead.
Another solution would be to return user.date_joined from get_user_join_date and somehow pass the custom default function to the JSON encoder used by whatever is processing that JWT payload.
It might also be possible to just return the date object from get_user_join_date, but only if the library you're using is smart enough to handle datetime objects (some are).