[Django]-Allow a user to vote only once. Django

Voter ids won’t necessarily fit your User ids. This explains why you see it sometimes appear to work (when voter id and user id accidentally match up). Replace:

voters = [user.id for user in Voter.objects.filter(poll__id=poll_id)]
if request.user.id in voters:

with

if Voter.objects.filter(poll_id=poll_id, user_id=request.user.id).exists()

It is better practice to let the database backend do the checks for you.