Hi Jairo,
Itzï was written at a time when GRASS was not supporting Python 3. Therefore, Itzï supports only Python 2.7.
The error you see is a typical Python 2 to 3 porting issue. Changing itervalues() to values() should solve this particular problem, but you will likely run into other similar issues.
Porting Itzï to Python 3 should not be very complex. Unfortunately I do not have to time to work on it now.
Help is welcome to port Itzï to Python 3. I would be more than happy to review a Pull Request on that matter.
In the mean time, the solution is to stick to Python 2.7.
Best regards,
Laurent