Python: if more than one of three things is true, return false

Question

I\'m writing a django model that allows my site to have coupons.

Coupons can have three types: lifetime account voucher, certain period of months voucher, certain numb

Answer 1

One thing I've done in similar situations is this:

coupon_types = (self.months, self.dollars, self.lifetime,)

true_count =  sum(1 for ct in coupon_types if ct)
if true_count > 1:
    raise ValueError("Coupon can be valid for only one of: months, lifetime, or dollars")  

It's now much easier to add new coupon types to check for in the future!