python 3.x - Problem with module import while running celery

Question

I do have code like that:

# tasks.py
from __future__ import absolute_import

import celery
from bs4 import BeautifulSoup
from dateutil import parser
from sqlalchemy.orm.exc import NoResultFound

from common import scraper as scraper
from common.printer import my_print as print  

class SqlAlchemyTask(celery.Task):
    """An abstract Celery Task that ensures that the connection the the
    database is closed on task completion"""
    abstract = True

    def after_return(self, status, retval, task_id, args, kwargs, einfo):
        db_session.remove()


@celery_app.task(base=SqlAlchemyTask, max_retries=10, default_retry_delay=60)
def download_task(url, date):
    # some code for my task...

When I try to run celery from command line

celery --app tasks worker -l DEBUG

I got this:

Usage: celery [OPTIONS] COMMAND [ARGS]...

Error: Invalid value for '-A' / '--app': 
Unable to load celery application.
While trying to load the module tasks the following error occurred:
Traceback (most recent call last):
  File "/home/mint/Dev/lib/python3.6/site-packages/celery/bin/celery.py", line 53, in convert
    return find_app(value)
  File "/home/mint/Dev/lib/python3.6/site-packages/celery/app/utils.py", line 384, in find_app
    sym = symbol_by_name(app, imp=imp)
  File "/home/mint/Dev/lib/python3.6/site-packages/kombu/utils/imports.py", line 56, in symbol_by_name
    module = imp(module_name, package=package, **kwargs)
  File "/home/mint/Dev/lib/python3.6/site-packages/celery/utils/imports.py", line 100, in import_from_cwd
    return imp(module, package=package)
  File "/home/mint/Dev/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/mint/Dev/data/downloader/tasks.py", line 8, in <module>
    from common import scraper as scraper
ModuleNotFoundError: No module named 'common'

My project looks like that:

── common
│   ├── const.py
│   ├── __init__.py
│   ├── scraper.py
├── data
│   ├── downloader
│   │   ├── celery.py
│   │   ├── db.py
│   │   ├── downloaderApp.py
│   │   ├── __init__.py
│   │   └── tasks.py
├── main.py

If I run my program from main.py everything works OK. I use virtualenv. If I run downloaderApp which has no imports everything works OK too:

# downloaderApp.py
from celery import Celery
import urllib.request
import os

# Where the downloaded files will be stored
BASEDIR="/home/celery/downloadedFiles"


broker_url = "amqp://localhost"
redis_url = "redis://localhost"
app = Celery(
    'downloaderApp',
    broker=broker_url,
    backend=redis_url)


@app.task
def download(url, filename):
    """
    Download a page and save it to the BASEDIR directory
      url: the url to download
      filename: the filename used to save the url in BASEDIR
    """
    response = urllib.request.urlopen(url)
    data = response.read()
    with open(BASEDIR+"/"+filename,'wb') as file:
        file.write(data)
    file.close()

@app.task
def add(x, y):
    return x + y

I tried with relative import (If I was doing that correctly), writing imports differently, shuffling them around but nothing works. What am I missing?