Python change UUID object to string representation list

Question

When retrieving a queryset with values_list of PKs there are of type UUIDField Django gives you a list of UUIDField objects and NOT a list of string UUIDs.

For example, the following gives me a query set:

items = Item.objects.values_list('id', flat=True).filter()

Where the output of print(items) is:

[UUID('00c8aa9e-2f61-4bac-320c-ab26b8fb1de9')]

But I would like the list to be a string representation of of UUID's i.e.

 ['00c8aa9e-2f61-4bac-320c-ab26b8fb1de9']

I can do this with each object individual in a loop but I want to change the whole queryset. Is this possible?

I have tried:

print(str(items))

Stephen Rauch · Accepted Answer · 2018-10-17 15:17:04Z

30

You can solve this in a Django specific way using the database instead of bringing the solution into memory.

Django now has the Cast function which can be imported from django.db.model.functions.

It can be then used in a query:

from django.db.models import TextField
from django.db.models.functions import Cast


items = Item.objects.annotate(str_id=Cast('id', output_field=TextField())).values_list('str_id', flat=True)

edited Oct 17, 2018 at 15:17

Stephen Rauch♦

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answered Oct 17, 2018 at 14:58

Andrew Miller

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1 Comment

scūriolus Over a year ago

Is there any reason for using a TextField() instead of a CharField()? Intuitively, the latter would have seemed more appropriate to me, given that the length of a uuid is 36 characters at most... But maybe it doesn't matter at all in terms of performance?

dsh · Accepted Answer · 2015-10-27 10:39:15Z

10

You have a list of objects that you want to convert to a list of strings:

items = [str(o) for o in items]

The only way to achieve that transformation is to process each item.

The reason print(str(items)) doesn't do what you want is that converts the list object to a string (which print() does anyway) rather than each object in the list.

answered Oct 27, 2015 at 10:39

dsh

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4 Comments

Prometheus Over a year ago

ok, I already got items = [str(o) for o in items] but is there no way at all?

Martin Thoma Over a year ago

Why do you want something else?

Prometheus Over a year ago

Good question, I'm not sure it just seems inefficient but I have no base for that statement.

dsh Over a year ago

This may be an XY Problem. Why do you want to convert your list of UUIDs to a list of strings? Any such conversion will be O(n) and thus "slow" for large amounts of data. It looks like you may be using django, so if you really want your data to be strings then there may be a different way of modeling it (in django and/or the database) as strings.

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