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

[Patrick Sathyanathan]

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