Wrapping an abstract class

[Shriramana Sharma]

The Cython docs don't say anything about wrapping C++ abstract base
classes, i.e. those with at least one member function of the type
virtual fn(args) = 0. It is desired that from Python one would create
a sub-class of such a class implementing all those methods declared
pure virtual in the base. Is this possible via Cython and is there
anything particular I should know about handling such classes?

--
Shriramana Sharma ஶ்ரீரமணஶர்மா श्रीरमणशर्मा

[Robert Bradshaw]

To simply wrap an abstract C++ class, you have to store a pointer
(just as you would when writing a C++ wrapper of a C++ abstract
class).

There's *experimental* support for extending C++ classes in Cython
with another C++ class:
https://github.com/cython/cython/blob/master/tests/run/cpp_classes_def.pyx
. You can't (yet?) actually extend a C++ class as a cdef class
accessible/further extendable from Python. (You can create a cdef
class that the C++ wraps and delegates all methods to manually
though.)

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[Shriramana Sharma]

On Thu, May 9, 2013 at 12:27 AM, Robert Bradshaw <robe...@gmail.com> wrote:
> . You can't (yet?) actually extend a C++ class as a cdef class
> accessible/further extendable from Python. (You can create a cdef
> class that the C++ wraps and delegates all methods to manually
> though.)

Hi and thanks for your reply. Do I then understand correctly that it
is (currently) not possible to *subclass* a C++ class within Cython,
and the workaround is to write a cdef class that *wraps* all its
members?

[Robert Bradshaw]

On Fri, May 17, 2013 at 8:26 PM, Shriramana Sharma <sam...@gmail.com> wrote:
> On Thu, May 9, 2013 at 12:27 AM, Robert Bradshaw <robe...@gmail.com> wrote:
>> . You can't (yet?) actually extend a C++ class as a cdef class
>> accessible/further extendable from Python. (You can create a cdef
>> class that the C++ wraps and delegates all methods to manually
>> though.)
>
> Hi and thanks for your reply. Do I then understand correctly that it
> is (currently) not possible to *subclass* a C++ class within Cython,

You can, see the above example, but you end up with another C++ class
that's not accessible from Python.

> and the workaround is to write a cdef class that *wraps* all its members?

If you want it to be visible from Python, yes. Cython is not a
wrapper-generator (though a great too to build one on).

- Robert