Does anyone know how I can test if an object's type is a builtin type or a user defined type ?

If it's not builtin, it must be imported from another module.

Yes, it's a good idea, for the most basic types. In fact the question is ambiguous. Types defined in C extension modules are not detected with this method. For example
but in fact the deque type lives in a C library _collections.so . I don't know how to detect this automatically.