PyCObject subtype PyObject

Michael Hudson mwh at python.net
Mon Jun 10 11:52:41 CEST 2002


Benjamin Tai <bt98 at doc.ic.ac.uk> writes:

> Hi,
> 
> 
> Any comments to clarify my confusion would be appreciated.
> 
> In Python/C API Reference Manual, section 7.5.9 CObjects,  the document
> mentions that:
> 
> "PyCObject This subtype of PyObject represents an opaque value, ..."
> 
> 
> 
> 1) What does it mean by "subtype"? As a C interface, is the document
> talking about two structs which share some common fields?

Yes.

> 2) For function "PyCObject_FromVoidPtr()", it takes in a "void*" as the
> first argument.
> For function "PyCObject_AsVoidPtr()", it returns a "void*".
> When implementing Python extension, what is the potential danger of
> casting pointers, of different size, to and from "void*"?

Doesn't C guarantee that you can cast a pointer of type (T*) to
(void*) and back again for all T?  I was fairly sure it did.

Python is implemented in C not C++, you know...

> 3) What if I can always determine the original type of the pointer?

Huh?

> 4) Apart from exporting function between modules, are there any
> examples of using PyCObject?

Not sure what you mean here either...

Cheers,
M.

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