[PyQt] SIP: deriving a python class from a C++ ABC results in a TypeError exception

[Demetrius Cassidy]

I think I answered my own question after re-reading the annotation docs.
Thanks.

On Sat, Jul 2, 2011 at 10:52 PM, Demetrius Cassidy <dcassidy36 at gmail.com>wrote:

> CCing mailing list
>
>
> On Sat, Jul 2, 2011 at 10:50 PM, Demetrius Cassidy <dcassidy36 at gmail.com>wrote:
>
>> On Sat, Jul 2, 2011 at 10:45 PM, Phil Thompson <
>> phil at riverbankcomputing.com> wrote:
>>
>>> On Sat, 2 Jul 2011 17:39:14 +0000, Demetrius Cassidy
>>> <dcassidy36 at gmail.com>
>>> wrote:
>>> > I have a C++ class which is declared with pure virtual methods, but if
>>> I
>>> > derive from this class in python and implement the pure virtual
>>> methods,
>>> I
>>> > get an exception:
>>> > TypeError: pyvoip.opal.OpalPCSSEndPoint cannot be instantiated or
>>> > sub-classed
>>> >
>>> > My python class is declared as following:
>>> >
>>> > class PCSSEndPoint(OpalPCSSEndPoint):
>>> >   def __init__(self):
>>> >   super(OpalPCSSEndPoint, self).__init__()
>>>
>>> That should be super(PCSSEndPoint, self).__init__()
>>>
>>
>>   The super thing was a typo.
>>
>>>
>>> > def OnShowIncoming(self, connection):
>>> > return True
>>> >
>>> > def OnShowOutgoing(self, connection):
>>> > return True
>>> >
>>> > def GetMediaFormats(self):
>>> >   return []
>>> >
>>> >
>>> > SIP definitions:
>>> >
>>> > class OpalPCSSEndPoint : OpalLocalEndPoint /Abstract/
>>> > {
>>> >
>>> > /**Call back to indicate that remote is ringing.
>>> > If false is returned the call is aborted.
>>> >
>>> > The default implementation is pure.
>>> > */
>>> > virtual PBoolean OnShowIncoming(
>>> > const OpalPCSSConnection & connection /NoCopy/ ///< Connection having
>>> event
>>> > ) = 0;
>>> >
>>> > /**Call back to indicate that remote is ringing.
>>> > If false is returned the call is aborted.
>>> >
>>> > The default implementation is pure.
>>> > */
>>> > virtual PBoolean OnShowOutgoing(
>>> > const OpalPCSSConnection & connection /NoCopy/ ///< Connection having
>>> event
>>> > ) = 0;
>>> >
>>> > };
>>> >
>>> > Now the base class of OpalPCSSEndPoint is also an ABC, as it derives
>>> from
>>> > an
>>> > ABC but does not re-define the pure virtual function:
>>> >
>>> > class OpalLocalEndPoint : OpalEndPoint /Abstract/
>>> > {
>>> >   ...
>>> > };
>>> >
>>> > class OpalEndPoint /Abstract/
>>> > {
>>> > virtual OpalMediaFormatList GetMediaFormats() const = 0;
>>> > };
>>> >
>>> > I tried removing  /Abstract/ from OpalLocalEndPoint, but it made no
>>> > difference.  Any idea what's wrong in this scenario? The only way this
>>> > works, is if I subclass OpalPCSSEndPoint in C++ and then in Python
>>> create a
>>> > class derived from my OpalPCSSEndPoint subclass.
>>>
>>> /Abstract/ is the cause of the problem. It doesn't mean that the C++ is
>>> an
>>> ABC, it means that the class contains other (unspecified) abstract
>>> methods.
>>>
>>> Phil
>>>
>>
>> So if /Abstract/ does not mean the class has pure virtual methods and
>> cannot be instantiated itself, in which scenario should it be used? I'm a
>> little confused here.
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.riverbankcomputing.com/pipermail/pyqt/attachments/20110702/88e67f81/attachment.html>