changes as suggested by @dianakhuang and @jbau

@chrisndodge Kindly review the changeset.

Thanks
You have a lot of extra code in the try/except block that obscures where you're expecting the exception could be raised. Why not do something like:
```python
try:
    coupon = Coupons.objects.get(id=coupon_id)
except ObjectDoesNotExist:
    # etc...
else:
    if coupon.is_active:
        # etc...
```