Update JSON element in Python List Comprehension

Question

Trying to update/add to a JSON element using if/then statement in python list comprehension. The first part where I'm setting the JSON key 'first_seen' is failing. Any ideas why?

now = datetime.datetime.now().strftime("%B, %d, %Y")
[obj["last_seen"] = now for obj in ref_db if obj['user']==user else add_new(user, ext_source, source, first_seen, now)]

the error is:

[obj["last_seen"] = now for obj in ref_db if obj['user']==user else add_new(user, ext_source, source, first_seen, now)]
                  ^
SyntaxError: invalid syntax

I understand from the error my syntax is wrong, but I can't figure out why it's wrong. Can you not use an equals (=) sign in a list comprehension?

Thanks for the help.

It's unclear what result you're expecting. Are you expecting `obj["last_seen"]` to be the resulting list? — jonrsharpe, Nov 04 '18 at 13:57
You need a plain if/else statement inside a for loop instead of a list comprehension — Carlos Mermingas, Nov 04 '18 at 13:58
Possible duplicate of [How can I do assignments in a list comprehension?](https://stackoverflow.com/questions/10291997/how-can-i-do-assignments-in-a-list-comprehension) — Carlos Mermingas, Nov 04 '18 at 14:00

score 4 · Accepted Answer · answered Nov 04 '18 at 14:00

List-Comprehensions are for creating lists. You just want to use a for-loop:

now = datetime.datetime.now().strftime("%B, %d, %Y")
for obj in ref_db:
    if obj['user'] == user:
        obj["last_seen"] = now
    else:
        add_new(user, ext_source, source, first_seen, now)

Update JSON element in Python List Comprehension

1 Answers1