[C++-sig] Trying to clone Python object from C++ (again)

[David Abrahams]

"Paul F. Kunz" <Paul_Kunz at slac.stanford.edu> writes:

>    I'm trying once again to clone a Python object whose class is
> derived from an exposed C++ base class from C++.  After I call from
> C++ clone() on the base class pointer, I wind up here...
>
> FunctionBase *
> FunctionWrap::
> clone () const
> {
> #ifndef HAVE_OLD_PYTHON
>   PyGILState_STATE state = PyGILState_Ensure ();
>   object py_result;
>
>   if (override clone = this->get_override("clone"))
>     {
>       try {
> 	// The Python class author overrode clone; do
> 	// whatever she says
> 	py_result = clone();
>       }
>       catch ( error_already_set & e ) {
> 	return 0;
>       }
>     }
>   else
>
> (thanks to Dave for essentially writing this for me).

I wrote that??  I wouldn't want to take responsibility for that
try/catch block.  It just discards all the information about what
happened.

> The problem is that the exception is thrown.   

Which exception?

> The Python code looks like...
>
> class Linear ( FunctionBase ) :
>     def __init__ ( self, other = None ) :
>         if other : # copy constructor
>             FunctionBase.__init__( self, other )
>         else : # default constructor
>             FunctionBase.__init__( self )
>             print "default called"
>             self.initialize ()
>
>     def clone ( self ) :
>         print "clone called"
>         return Linear ()
>     
> Where FunctionBase is the exposed C++ class.   Both print states are
> executed when I call clone() from C++.
>
> Suggestions?

  if (override clone = this->get_override("clone"))
  {
        // The Python class author overrode clone; do
        // whatever she says
        py_result = clone();
  }
  else

??

Or, at the very least,

  if (override clone = this->get_override("clone"))
  {
        // The Python class author overrode clone; do
        // whatever she says
        try { py_result = clone(); }
       catch ( error_already_set & e ) { PyErr_Print(); return 0  }
  }
  else


-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com