simple integer subclass

[Carl Banks]

On Aug 2, 4:52 pm, Andreas Pfrengle <a.pfren... at gmail.com> wrote:
> I'm trying to define a subclass of int called int1. An int1-object
> shall behave exactly like an int-object, with the only difference that
> the displayed value shall be value + 1 (it will be used to display
> array indices starting at 1 instead of 0). Right now I have:
>
> class int1(int):
>     def __str__(self):
>         return int.__str__(self + 1)
>
> However, if I calculate with int1 and int- (or other number) objects,
> the result is always coerced to an int (or other number object), e.g:
> a = int1(5)
> b = 5
> print a      # "6"
> print a+b  #"10"
>
> How can I tell int1 to be the "default integer object"? Do I need to
> overload *every* mathematical operation method of int, or is there an
> easier way?

(Preface: I normally don't offer recommendations without answering the
question as asked, but once in a while it has to be done.)

I **highly** recommend against this approach.

You are creating an object that differs from a built-in, int, in a
highly misleading way that only makes sense in a very limited context,
and this object's modified behavior gives no clue that it's been
modified in such as way.  (That is, it's not possible to tell if the
object's not a regular int just by looking at __str__()'s return
value.)  To make matters worse, you want to program this object to
coerce other integers, so there's a risk of these objects escaping
from the context where they make sense.

This is just a bad idea.  The type is not the place to implement
behavior that makes sense only in a limited context.  Instead, do
something like this:

print "Item %d is %s." % (i+1, s[i])


Carl Banks