Yet another Python import question sorry….

I am using Flask and use Heroku in production
Everything is working great on my laptop, but impossible to make it work when I push it to Heroku

Here is my directory hierarchy from the root directory :

__init__.py (empty)
app.py
Procfile
sub1/
----__init__.py (empty)
----sub2/
--------__init__.py (empty)
--------file.py

My app.py :

from sub1.sub2.file import Myclass
x = Myclass()

My sub1/sub2/file.py file :

class Myclass():
    # Some code

My Procfile :

web: gunicorn app:app

Everything is working great on my laptop but as soon as i push it to Heroku I get the error :

ModuleNotFoundError: No module named 'sub1.sub2.file'

I have tried relative import with from .sub1.sub2.file import Myclass but I get the error :
ImportError: attempted relative import with no known parent package

I have also tried to :

• import sub1 as sub1 inside app.py
• x = sub1.sub2.file.Myclass() inside app.py
• add from . import sub2 inside sub1/__init__.py
• add from . import file inside sub1/sub2/__init__.py
• but still not working

I have also tried to add the folders in the sys.path :

base_dir = os.path.dirname(os.path.abspath(__file__))
sys.path.append(base_dir)
sys.path.append(os.path.join(base_dir, 'sub1'))
sys.path.append(os.path.join(base_dir, 'sub1', 'sub2'))
from sub1.sub2.file import Myclass

Once again, each solution works on my laptop when I do python app.py or foreman start -f Procfile but never works on Heroku… is it even possible ?