when I run the Flask Server with flask run, I get error 404 in the Index Page.
* Serving Flask app "sf.py"
* Environment: production
WARNING: This is a development server. Do not use it in a production deployment.
Use a production WSGI server instead.
* Debug mode: off
* Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
127.0.0.1 - - [18/Feb/2021 10:25:56] "GET / HTTP/1.1" 404 -
Not Found
The requested URL was not found on the server. If you entered the URL
manually please check your spelling and try again.
Project Structure
.
├── app
│ ├── models.py
│ ├── routes.py
│ └── __init__.py
├── clients
│ └── client.py
├── migrations
├── tests
│ ├── conftest.py
│ ├── test_models.py
│ ├── test_client.py
│ └── __init__.py
├── publisher.py
├── manage.py
├── run_client.py
├── requirements.txt
└── sf.py
/sf.py
from app import create_app
create_app()
/app/__init__.py
from flask import Flask
from . models import db
POSTGRES = {
'user': 'sf',
'pw': 'sf',
'db': 'sf',
'host': 'localhost',
'port': '5432',
}
def create_app():
app = Flask(__name__)
app.config['DEBUG'] = True
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://%(user)s:%(pw)s#%(host)s:%(port)s/%(db)s' % POSTGRES
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
db.init_app(app)
return app
from app import routes
/app/routes.py
from app import create_app
from app.models import Area, Sensor, Monitoring
from flask import request, jsonify
from flask.views import MethodView
app = create_app()
#app.route('/')
def hello_world():
return 'Hello, World!'
...
I need to use the create_app() because I need an that the /clients/client.py use the app.
/clients/client.py
from paho.mqtt.client import Client
import json
from app import create_app
from app.models import db
from app.models import Monitoring
app = create_app()
class CustomClient(Client):
def add_reading(self, reading):
with app.app_context():
db.session.add(reading)
db.session.commit()
def on_connect(self, client, userdata, flags, rc):
print(
"Connected:",
str(client._host) + ":" + str(client._port)
)
def on_subscribe(self, mqttc, obj, mid, granted_qos):
print(
"Subscribed:",
str(mid), str(granted_qos)
)
def on_message(self, client, userdata, message):
msg = message.payload.decode()
print(message.topic, msg)
data = json.loads(msg)
reading = Monitoring(**data)
self.add_reading(reading)
def run(self):
self.connect("localhost", 1883, 60)
self.subscribe("Main/#", 0)
self.loop_forever()
But in this way I get the 404 error. And I'm not sure that I'm using the app properly. It would be fine to have an app and a db session separate, to test models and client without care the app configuration (probably I need to create a separate config for test?). What I've missed?
You are creating three instances of the Flask() object. One is created in sf.py, the others in routes.py and client.py. The first one is used to serve the site, and so doesn't have your route, because the route is registered with the instance created in routes.py. The 3rd instance, in client.py is independent and isn't further altered, so is not an issue here; more on that below.
Don't create multiple copies, at least not and alter the registrations on one and expect those to be available on the other. Instead, use blueprints to register your views, and then register the blueprint with the Flask() object in your create_app() function. That way you can decouple registration of your routes from creating the Flask() object, and still get your routes registered centrally.
In your routes.py, use:
from app.models import Area, Sensor, Monitoring
from flask import Blueprint, request, jsonify
from flask.views import MethodView
bp = Blueprint('main', __name__)
#bp.route('/')
def hello_world():
return 'Hello, World!'
# ...
and then import that blueprint in create_app():
def create_app():
app = Flask(__name__)
app.config['DEBUG'] = True
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://%(user)s:%(pw)s#%(host)s:%(port)s/%(db)s' % POSTGRES
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
db.init_app(app)
from . import routes
app.register_blueprint(routes.bp)
return app
The reason you want to do the import in create_app() is that in most Flask applications you'll also be using one or more Flask extensions that are generally created outside of create_app() so your views can import them. You'd get a circular import if you tried to import one of those objects in your routes module if your routes module was imported into app.py at the top level.
With this change (to using a blueprint), you avoid creating a separate Flask() instance with registrations that the main instance, used for serving your site, won't see. Even your client.py process will be able to access those routes now, should there be a need (e.g. if you need to generate URLs with url_for()).
Here is an example from an in-production Flask project I built for a client recently, the app.py module contains, in part, the following code:
from flask import Flask
from flask_babel import Babel
from flask_marshmallow import Marshmallow
from flask_migrate import Migrate
from flask_security import Security, SQLAlchemyUserDatastore
from flask_sqlalchemy import SQLAlchemy
babel = Babel()
db = SQLAlchemy()
ma = Marshmallow()
migrate = Migrate()
security = Security()
_app_init_hooks = []
app_init_hook = _app_init_hooks.append
def create_app():
app = Flask(__name__)
for f in _app_init_hooks:
f(app)
return app
#app_init_hook
def _configure(app):
"""Load Flask configurations"""
app.config.from_object(f"{__package__}.config")
# optional local overrides
app.config.from_pyfile("settings.cfg", silent=True)
app.config.from_envvar("PROJECT_NAME_SETTINGS", silent=True)
#app_init_hook
def _init_extensions(app):
"""Initialise Flask extensions"""
if app.env != "production":
# Only load and enable when in debug mode
from flask_debugtoolbar import DebugToolbarExtension
DebugToolbarExtension(app)
# Python-level i18n
babel.init_app(app)
# Database management (models, migrations, users)
from .models import Role, User
db.init_app(app)
migrate.init_app(app, db)
user_datastore = SQLAlchemyUserDatastore(db, User, Role)
security.init_app(app, user_datastore)
# Marshmallow integration (must run after db.init_app())
ma.init_app(app)
#app_init_hook
def _setup_blueprints(app):
"""Import and initialise blueprints"""
from . import users
from .sections import BLUEPRINTS
for blueprint in (*BLUEPRINTS, users.bp):
app.register_blueprint(blueprint)
return app
I've broken up the various components into separate functions to ease readability and maintainability, there are separate blueprints used for distinct site functions (which drives some automation in the UI).
At the top of the module are several Flask extensions that various routes and other modules need access to without having to worry about circular imports, so the blueprints are imported separately inside of the _setup_blueprints() hook function that is called from create_app().
Your use of create_app() in client.py should be fine because it doesn't add any new configuration to the Flask() instance that you'd want to have access to elsewhere, and presumably client.py is used outside of the Flask webserver process. But I would, personally, just make the result of create_app()an instance attribute of your Client instance. You don't need a global there, you only need it to access the database session easily for when add_reading() is called:
class CustomClient(Client):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs):
# Create a Flask context so we can access the SQLAlchemy session
self._app = create_app()
def add_reading(self, reading):
with self._app.app_context():
db.session.add(reading)
db.session.commit()
# ...
If add_reading() is called very frequently, you could consider making app an instance attribute of CustomClient():
I am learning flask. I have a directory structure that looks something like this.
project
- controllers
-- auth.py
-- main.py
- db
-- setup.py
- models
-- models.py
- templates
-- base.html
-- index.html
-- login.html
-- signup.html
-- 404.html
-__init__.py
The file init.py looks like this
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
# init SQLAlchemy so we can use it later in our models
db = SQLAlchemy()
def create_app():
app = Flask(__name__)
app.config['SECRET_KEY'] = '9OLWxND4o83j4K4iuopO'
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://root:#localhost/mission_to_mars'
db.init_app(app)
# blueprint for auth routes in our app
from .controllers.auth import auth as auth_blueprint
app.register_blueprint(auth_blueprint)
# blueprint for non-auth parts of app
from .controllers.main import main as main_blueprint
app.register_blueprint(main_blueprint)
return app
I'm trying to import the db variable and create_app() function in controllers/auth.py, controllers/main.py, models/models.py, db/setup.py
I have tried the below syntaxes
from .. import db, create_app
which gives the error:
ImportError: attempted relative import with no known parent package
I have also tried
from project import db, create_app
which gives the error
ModuleNotFoundError: No module named 'project'
I want to know how I can import classes from different directories so that I can use them further in the project.
Thanks in advance
I've rummaged through maybe 50 different answers to this and still I haven't manage to fix it... I'm pretty new to flask and python.
I have an app which was running great locally but I've struggled with deploying on python anywhere. Initially I had a few import modules issues, now it runs but doesn't return any html template, despite not seeing any other issue. The main issue I had was that it couldn't find the "routes" app from wsgi, and I sort of fixed adding the app = Flask(name) line on routes.py (the short blueprint object is not callable).
routes.py:
from flask import Blueprint, render_template, request, redirect, send_file
import pyqrcode
from pyqrcode import QRCode
import subprocess
from extensions import db
from models import Link
app = Flask(__name__)
short = Blueprint('short', __name__, url_prefix='/')
#short.route('/index')
def index():
return render_template('index.html')
init.py
from flask import Flask
from extensions import db
from routes import short
def create_app(config_file='settings.py'):
app = Flask(__name__)
app.config.from_pyfile(config_file)
db.init_app(app)
app.register_blueprint(short)
return app
wsgi.py
import sys
# add your project directory to the sys.path
project_home = u'/home/b297py/mysite'
if project_home not in sys.path:
sys.path = [project_home] + sys.path
# import flask app but need to call it "application" for WSGI to work
from routes import app as application
For the purpose of testing, I've placed all the html templates both in the root directory and in the specific /template directory but it just didn't fix the issue.
In wsgi.py you are not calling create_app so you are never registering the blueprint. You should replace :
from routes import app as application
by something like :
from package_name import create_app
application = create_app()
(Example: https://www.pythonanywhere.com/forums/topic/12889/#id_post_50171)
Also as you mentioned, the fix adding app = Flask(__name__) to routes.pyallows you to bypass create_app (so you should remove it if you want to stick to the create_app approach).
I'm trying to write tests for a simple Flask application. Structure of the project is following:
app/
static/
templates/
forms.py
models.py
views.py
migrations/
config.py
manage.py
tests.py
tests.py
import unittest
from app import create_app, db
from flask import current_app
from flask.ext.testing import TestCase
class AppTestCase(TestCase):
def create_app(self):
return create_app('test_config')
def setUp(self):
db.create_all()
def tearDown(self):
db.session.remove()
db.drop_all()
def test_hello(self):
response = self.client.get('/')
self.assert_200(response)
app/init.py
# app/__init__.py
from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy
from config import config
db = SQLAlchemy()
def create_app(config_name):
app = Flask(__name__)
app.config.from_object(config[config_name])
db.init_app(app)
return app
app = create_app('default')
from . import views
When I launch the tests, test_hello fails because response.status_code is 404. Tell me, please, how can I fix it? It seems, that app instance doesn't know anything about view functions in the views.py. If it needs the whole code, it can be found here
Your views.py file mount the routes in the app created in your __init__.py file.
You must bind these routes to your created app in create_app test method.
I suggest you to invert the dependency. Instead the views.py import your code, you can make a init_app to be imported and called from your __init__.py or from the test file.
# views.py
def init_app(app):
app.add_url_rule('/', 'index', index)
# repeat to each route
You can do better than that, using a Blueprint.
def init_app(app):
app.register_blueprint(blueprint)
This way, your test file can just import this init_app and bind the blueprint to the test app object.
My app layout
my_app
__init__.py
my_app
__init__.py
startup
create_app.py
create_users.py
common_settings.py
core
models.py
views.py
Inner __init__.py
from flask import Flask
from flask_script import Manager
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__) # The WSGI compliant web application object
db = SQLAlchemy(app) # Setup Flask-SQLAlchemy
manager = Manager(app) # Setup Flask-Script
from my_app.startup.create_app import create_app
create_app()
create_app.py
from native_linguist_server import app, db
#app.before_first_request
def initialize_app_on_first_request():
""" Create users and roles tables on first HTTP request """
from .create_users import create_users
create_users()
def create_app(extra_config_settings={}):
app.config.from_envvar('ENV_SETTINGS_FILE')
# Load all blueprints with their manager commands, models and views
from my_app import core
return app
When I run my app like this and try to load a view in my browser, I get a 404 error.
However if I change:
from my_app import core
to
from my_app.core import views
it works fine.
Could someone please explain to me the difference between these two calls? I would have thought from my_app import core would also import views.py and hence there wouldn't be an issue.
Thank you.
from my_app import core
will load and execute my_app/core/__init__.py (if it exists). You will then have access to any identifiers defined inside or imported into __init__.py.
from my_app.core import views
will load and execute my_app/core/views.py. You'll then have access to any identifiers defined inside or imported into views.py.
To get the behavior you're expecting, you'll need to import views inside __init__.py:
from . import views