If this is my fault the docs need to be more explanatory, but here's the problem: for the sequence (0, 1, 2), the Boost::Python iterator starts at 1 and ends 1 past 2 ( where 3 might be ). It does this because it calls the C++ iterators functions in this order: operator == post-increment dereference It should imho call them like (which would correct the issue) operator == dereference post-increment Like a normal for loop would execute: condition, code, action. The code to reproduce this is: #include <iterator> #include <boost/python.hpp> namespace py = boost::python; struct ctn { struct iterator: public std::iterator< std::input_iterator_tag, py::str > { int mNum; iterator( int num = 0 ): mNum( num ) {} py::str operator *() const { char temp[20]; const char * str = itoa( mNum, temp, 10 ); return py::str( str, strlen( str ) ); } iterator& operator ++(int) { mNum++; return *this; } friend bool operator ==( iterator lhs, iterator rhs ) { return ( lhs.mNum == rhs.mNum ); } }; iterator begin() { return iterator( 0 ); } iterator end() { return iterator( 3 ); // the range (0, 1, 2) three items } }; BOOST_PYTHON_MODULE(iter_bug) { py::class_< ctn >( "ctn" ) .def( "__iter__", py::iterator< ctn >() ) ; }
from iter_bug import * c = ctn() for i in c: ... print i ... 1 2 3
Notice how it's off by one because of the very strange order of doing things. Please help! -Dan