Method init

include/pybind11/pytypes.h:1589–1594

private:
    void init() const {
        if (m_ptr && !value.ptr()) {
            auto &self = const_cast<iterator &>(*this);
            self.advance();
        }
    }

    void advance() {
        value = reinterpret_steal<object>(PyIter_Next(m_ptr));