Re: [boost] py_cpp: isinstance with extension classes

From: Anton Gluck (gluc_at_[hidden])
Date: 2000-11-27 01:04:46

Dave,

> I suggest writing isinstance() in Python something like this.
> 
> # untested! (not needed For Python 2.0)
> def _is_subclass(t1, t2):
>     for b in getattr(t1. '__bases__', ()):
>         if b is t2 or _is_subclass(b, t2):
>             return 1
>     return 0
> 
> # untested! For Python 1.5 or 2.0
> def is_instance(obj, type):
>     return isinstance(obj, type) or _is_subclass(getattr(obj, '__class__',
> None), type)

I tried my luck with a very simple version of a custom isinstance(). I
wrote it like this:

def _is_instance(object, extensionclass):
    if object.__class__ == extensionclass:
        return 1
    else:
        return 0

This uses the built-in repr() for extensionclass, which will match an
object's __class__ if it is an instance of that extensionclass. This
worked for simple test cases, but unfortunately not for the purpose I
needed this for. My problem is that I have a vector of ClusterVars, where
each object is of type ClusterVar, and not of type CatVar or ContVar
anymore. Somewhere along the way I lost that information. Once I figure
out how to get back the original type, I hope the above code will do the
trick for me.

Thanks,

Toni