subclass of integers

[Mark Morss]

On Sep 14, 10:30 am, Mark Morss <mfmo... at aep.com> wrote:
> I would like to construct a class that includes both the integers and
> None.  I desire that if x and y are elements of this class, and both
> are integers, then arithmetic operations between them, such as x+y,
> return the same result as integer addition.  However if either x or y
> is None, these operations return None.
>
> It's simple enough to construct a subclass of integers that behave in
> this way:
>
> class Nint(int):
>     def __add__(self,other):
>         if (other != None):
>             return self+other
>         else:
>             return None
>     def __radd__(self,other):
>         if (other != None):
>             return other+self
>         else:
>             return None
>     #...and so forth
>
> However I have not been able to figure out how to make it so that
> None, as well as an integer, could be an element of my class.  My
> preliminary impression is that I have to override int.__new__; but I
> am uncertain how to do that and have been unable to find anything on
> the web explaining that.  Indeed I haven't been able to find much
> about __new__ at all.  Overriding this method of built-in classes
> seems to be quite unusual.
>
> I would very much appreciate anyone's help.

I meant of course that arithmetic operations between integer elements
would return the same result as the corresponding integer operations,
not necessarily addition.