[Tutor] Python 3.4.1 ImportError Linux

[Juan Christian]

Python 3.4.1
Fedora 21 Server

My paths:
~/lorem
~/lorem/app
~/lorem/core

I want to execute: ~/lorem/app/main.py

Terminal (~/lorem/app): python3 main.py

Traceback (most recent call last):
File "app/main.py", line 5, in <module>
from core.backpack import BackpackThread
ImportError: No module named 'core'


Why am I getting this?