In Django/Python how to handle exception - list index out of range for empty table?

Question

My problem is that when my Database is empty I am getting this error

IndexError at / list index out of range

>  period = Period.objects.all()
>     try:
>         period_current = [obj for obj in period if ((obj.is_current)==True)]
>                     total_payment_period_current_dict = LeasePayment.objects.filter(payment_date__range=[period_current[0].start_date,
> period_current[0].end_date]).aggregate(Sum('amount')) ...
>         total_payment_period_current = total_payment_period_current_dict['amount__sum']
>     except ValueError:
>         raise Http404("Can't perform calculation for total_payment_period_current, check data ")

I hoped I can handle it with exeption to give meaningful error , but it doesn't work. What I can do to give meaningful error . Or ideally to avoid this exception all together in case of empty tables?

Arpit Solanki · Accepted Answer · 2017-08-26 14:25:47Z

If you want to handle this error then I would suggest putting a check for length of list.

try:
    period_current = [obj for obj in period if ((obj.is_current)==True)]
    if len(period_current == 0) {
       raise Http404("Can't perform calculation for total_payment_period_current, check data ") 
    }
    total_payment_period_current_dict = LeasePayment.objects.filter(payment_date__range=
                                  [period_current[0].start_date,
                period_current[0].end_date]).aggregate(Sum('amount')) 
         total_payment_period_current = total_payment_period_current_dict['amount__sum']
     except ValueError:
         raise Http404("Can't perform calculation for total_payment_period_current, check data ")

This is a wrong exception for your case. You might want to use IndexError exception instead of ValueError exception.

except IndexError:
    raise Http404("Can't perform calculation for" +
                  "total_payment_period_current, check data ")

This answer might be helpful to you to understand the problem.

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