[C++-sig] pyplusplus bug related to boost::equality_comparable (and possibly other operators as well)

Jakub Zytka kubol at kormoran.net
Thu Sep 9 13:50:18 CEST 2010

Actually, I haven't had time to investigate it deeper yet, but it seems to be a 
pyplusplus's bug. I also haven't found anything relevant on the net, so here we go:

Test case:
class to be exposed (file a.h)

#include <boost/operators.hpp>

class A: boost::equality_comparable<A>
         A(int a): a(a) {};

         bool operator==(A const & other) const
                 return this->a == other.a;
         int a;

generator used (gen.py):
from pyplusplus import module_builder

mb = module_builder.module_builder_t(files = ['a.h'])


mb.build_code_creator( module_name = 'testA')

file generated:
// This file has been generated by Py++.

#include "boost/python.hpp"

#include "a.h"

namespace bp = boost::python;

     { //::A
         typedef bp::class_< A > A_exposer_t;
         A_exposer_t A_exposer = A_exposer_t( "A", bp::init< int >(( 
bp::arg("a") )) );
         bp::scope A_scope( A_exposer );
         bp::implicitly_convertible< int, A >();
         A_exposer.def( bp::self == bp::self );
	// OOPS! something is missing here

C++ class test:
#include <iostream>
#include "a.h"

using namespace std;

int main()
         A a1(3);
         A a2(3);
         cout << "a1 == a2: " << (a1 == a2) << endl;
         cout << "a1 != a2: " << (a1 != a2) << endl;
         return 0;

C++ class test result:
a1 == a2: 1
a1 != a2: 0

python test:
 >>> import testA
 >>> a1 = testA.A(3)
 >>> a2 = testA.A(3)
 >>> a1 == a2
 >>> a1 != a2
True # drat!

The reason: missing A_exposer.def( bp::self != bp::self ); in the generated code;

If any of you think it is easy to fix in pyplusplus (Roman, perhaps you're the 
one to know best?) I may try. I'm also considering a workaround of checking 
bases for all the classes and add missing "self != self" for all those which 
derive from equality_comparable;
Perhaps there is the same problem with less_than_comparable and others.


More information about the Cplusplus-sig mailing list