[Python-Dev] PyInstance_Check() and new-style classes

Phillip J. Eby pje at telecommunity.com
Mon Jul 12 15:48:19 CEST 2004

At 08:11 PM 7/11/04 -0500, Eric Wilhelm wrote:

>So, is PyInstance_Check() supposed to work, or is there some PyFoo_Check()
>function that will work?

No, to both questions.

>It seems really wrong to have to add-up all of the other types and use this
>process of elimination to identify a new-style class instance.

As of 2.2, *all* Python types *except* InstanceType may be considered to be 
"new-style class instances".

If you want to find out whether a type was defined in Python or C, you can 
use the "heap type" flag in the type structure.  Note, however, that this 
will not let you distinguish between core C types and C extension types, so 
using it might be a bad idea if the reason you're using Python is to use a 
Python module written in C!

>  Also, it
>seems that it would fail if a class inherited from a built-in type.  I'm
>almost sure that I'm way off-course, so if anyone could put me on track, I'd
>really appreciate it.

Why do you want to distinguish between different kinds of objects?  Is it 
because Perl needs/wants Python strings and numbers to become 
scalars?  Perhaps you should simply convert those types that you want an 
exact conversion for, and consider everything else to be 
"instances".  Better yet, provide a way for the user to define Perl 
mappings for specific Python types, which would give more flexibility in 
bridging the two, or require explicit conversion operations.  Or perhaps 
you could use Perl contexts in some way to decide what type of conversion 
should take place?

(Also, isn't there a Python::Object package out there?  What does it 
do?  Has it been updated for Python 2.2?)

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