About python relative importing

Relative importing is painful

The relative importing has always been painful in python. For example, we are writing a web app using Flask. The file structure is like following:

\root
	run.py
	\views
		blueprint.py

To use websocket, we have chosen the flask-socketio. In the run.py and our blueprint file, we all need the socketio variable. It is natural for one to write the following code:

In run.py

... ...
from flask-socketio import SocketIO
... ...
socketio = SocketIO()

def register_blueprint(app):
    ... ...
    
app = Flask(__name__)
register_blueprint(app)

socketio.init_app(app)
... ...

And in blueprint.py

from ..run import socketio

... ...
@socket.on('message'):
	... ...

But this would trigger:

Error: attempted relative import beyond top-level package

Decent solution

We need to move the variable socketio to __ init__.py. Now the file structure is:

\root
	run.py
	\views
		__init__.py
		blueprint.py

In __ init__.py:

socketio = SocketIO()

In run.py

from views import socketio

In blueprint.py

from . import socketio

Problem solved!