Re: [Discuss-gnuradio] Calling C++ method from Python

[Patrick Sathyanathan]

Thanks much, Marcus. That was the issue. I had missed adding the declarations for the callbacks in the non-impl class. As in the analog signal source block, just adding pure virtual function declarations for the callbacks did the trick.
 
I'm not familiar with SWIG and I don't know why this works. But I'm happy it does without having to dig into SWIG details.
 
Thanks,
 
--Patrick
 

> Date: Mon, 6 Jul 2015 09:53:16 +0200
> From: address@hidden
> To: address@hidden
> Subject: Re: [Discuss-gnuradio] Calling C++ method from Python
>
> Hi Patrick,
>
> the typical problem with C++ blocks is that people add public methods to
> their _impl, but forget to declare these same methods in their public
> non-impl class.
> Have you done the same expand magic with the header in your
> include/CMakeLists.txt?
>
> Best regards,
> Marcus
>
>
> On 07/06/2015 04:09 AM, Patrick Sathyanathan wrote:
> > Hi,
> >
> > I have worked my way through the Guided Tutorials on gnuradio.org. I have written OOT blocks in Python and managed to expose some set methods in the block as callbacks. Now I have written an OOT C++ block sweeper_cpp_f and I want to expose a couple of setter methods in my block's class as callbacks that can be invoked from Python. Initially I just defined the methods in my sweeper_cpp_f_impl.cc file and added the following to the matching XML file:
> >
> > <callback>set_direction($direction)</callback>
> > <callback>set_trigger_level($trigger_level)</callback>
> >
> > This builds fine and I am able to use the block in a GRC flow-graph. But at runtime when one of the above methods is invoked as a result of GUI input I get an error message:
> >
> > File "/home/wpats/ettus/grc/new_sweep_cpp.py", line 141, in set_variable_chooser_direction
> > self.tutorial_sweeper_cpp_f_0.set_direction(self.variable_chooser_direction)
> > AttributeError: 'sweeper_cpp_f_sptr' object has no attribute 'set_direction'
> >
> > I looked at built in module sig_source_X_impl.h.t and sig_source_X_impl.cc.t (this is the analog signal source block) in gr-analog as an example for what I am trying to accomplish. I converted my sources into a similar format and modified the CMakeLists.txt in the .../gr-tutorial/lib directory to add:
> >
> > ########################################################################
> > # Invoke macro to generate various sources and headers
> > ########################################################################
> > include(GrMiscUtils)
> > GR_EXPAND_X_CC_H(tutorial sweeper_cpp_X_impl f)
> >
> > This again builds fine after I edit the generate_helper.py generated script to find an import module. I assumed that the above would do the necessary magic to generate the wrappers for my callback methods but no such luck. I still get the attribute error when invoking my C++ method.
> >
> > What is the right way to do this ? Any help/suggestions/pointers would be appreciated. I can't be the first one to try to do this seemingly simple task...
> >
> > Thanks,
> >
> > --Patrick
> >
> >
> > _______________________________________________
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>
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