Attempting to iterate over python iterable, in c++, iterates past the end with bound c++ types.

[ariaTim]

Issue

Attempting to iterate over python iterable, in c++, iterates past the end with bound c++ types. It seems that comparing the end iterator to the sentinel attempts to advance the end iterator past the end. When iterating a python type calling PyIter_Next past the end simply returns NULL however for a bound STL container this invokes undefined behaviour.

Occurs on:
Windows 10 (VS 2017), Ubuntu 17.04 (gcc 7.0)
pybind11 2.1.1 and master ( 0365d49 )

Example

cpp:

#include <pybind11/pybind11.h>
#include <pybind11/stl_bind.h>

namespace py = pybind11;

PYBIND11_MAKE_OPAQUE(std::vector<int>)

PYBIND11_MODULE(IterableTest, m)
{
    py::bind_vector<std::vector<int>>(m, "VectorInt");

    m.def("iter_test", [] (py::iterable iterable)
    {
        auto iter = py::iter(iterable);
        while (iter != py::iterator::sentinel())
        {
            py::print("got value: ", *iter);
            ++iter;
        }
    });
}

python:

from IterableTest import *

ivec = VectorInt()
ivec.append(3)
ivec.append(2)
ivec.append(1)

iter_test(ivec)

example output:

got value:  3
got value:  2
got value:  1
*debug assert iterator is not incrementable*

[dean0x7d]

Thanks for reporting the bug! Should be fixed in #897.