myproject/
    common/
        __init__.py
        model.py
    alembic/
        env.py

from .common import model
SystemError: Parent module '' not loaded, cannot perform relative import

. ← That's the root directory of my project
├── alembic.ini
├── dev-requirements.txt
├── requirements.txt
├── runtime.txt
├── setup.cfg
├── src
│   └── models
│       ├── base.py
│       ...
│       └── migrations
│           ├── env.py
│           ├── README
│           ├── script.py.mako
│           └── versions
│
└── tests

import sys
from os.path import abspath, dirname
sys.path.insert(0, dirname(dirname(dirname(abspath(__file__))))) # Insert <.>/src
import models # now it can be imported
target_metadata = models.base.Base.metadata

PYTHONPATH=. alembic revision -m "..."

from src.models.base import Base

import sys
import os

sys.path.insert(0, os.getcwd())