Python Django loop logic: Error says 'int' is not iterable - check my syntax?

Question

return sum(jobrecord.get_cost() or 0 
    for jobrecord in self.project.jobrecord_set.filter(
        date__lte=date,
        date__gte=self.start_date) or 0)

Answer 1

After a small rewrite

query = self.project.jobrecord_set.filter(
        date__lte=date,
        date__gte=self.start_date)
values= ( jobrecord.get_cost() or 0 for jobrecord in query or 0 )
return sum( values )

Look closely at the values= ( jobrecord.get_cost() or 0 for jobrecord in query or 0 )

What happens when the query is empty?

You're evaluating jobrecord.get_cost() or 0 for jobrecord in 0

Answer 2

Mr. Lott!

Thank you. What if put the or 0 on the outside of the parenthesis, as below?

return sum(jobrecord.get_cost() or 0 
    for jobrecord in self.project.jobrecord_set.filter(
        date__lte=date,
        date__gte=self.start_date)) or 0

Answer 3

0 is indeed not iterable. I think you want to drop that last or 0. when the filter query matches no elements, it will return an empty query, and your sum will just be 0, since sum([]) is zero.

If there's some reason why the query might raise an exception (invalid dates or some such), an or clause wont catch that either. [][1] or 0 still raises an exception.