[Tutor] use of __new__

[A.T.Hofkamp]

spir wrote:
> Hello,
> 
> I have (again) some issue using __new__.
> What I need is basically to catch an object creation and yield an object of an alternate type, when a condition is met.
> 
> Basically, the outline looks like:
> 
> class Normal(object):
>     def __new__(cls, arg):
>         if cond(arg):
>             # <yield instance of Special>
>             # expression is simply: Special(arg)
>             # must be __init__ialised !
>         
>         # Conceptually, nothing to change:
>         # <yield instance of Normal>
>         # must be __init__ialised !
> 
> But I got issues in both cases:
> * cannot find how to get Special objects initialised
> * cannot find how to return Normal object
> (also Normal's supertype has no explicite __new__, but it has an __init__)

Maybe it's just me, but why don't you use a factory function?

def make(args):
   if cond(args):
     return Special(args)
   else:
     return Normal(args)


Albert