examples/package/use_project/proj1_2.py
from __future__ import print_function
import sys, os
sys.path.insert(0, os.path.join(
    os.path.dirname(os.path.dirname(os.path.abspath(__file__))),
    '1' ) )

import mymath
print(mymath.calc.add(4, 7))
Traceback (most recent call last):
  File "proj1_2.py", line 6, in 
    print(mymath.calc.add(4, 7))
AttributeError: 'module' object has no attribute 'calc'

If we import the main package name, it does not have access to the module inside.