[semidet]py_is_object(@Term)True when Term is a Python object reference. Fails silently 
if Term is any other Prolog term.
- Errors
 existence_error(py_object, Term) is raised of Term 
is a Python object, but it has been freed using py_free/1. 
- Compatibility
 - PIP. The SWI-Prolog implementation is safe in the sense that an 
arbitrary term cannot be confused with a Python object and a reliable 
error is generated if the references has been freed. Portable 
applications can not rely on this.