I have multiple apps and use flask_sqlalchemy with the style below:
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
def create_app():
app = Flask(__name__)
db.init_app(app)
return app
However, in the test, all the app linked to the same database.
after I switch to the following style. Every app can linked to its own database.
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
def create_app():
app = Flask(__name__)
with app.app_context():
db.init_app(app)
return app
I did not understand why? If the second case is better, why it is not in the official doc?
credit: I copied the second style from https://hackingandslacking.com/demystifying-flasks-application-context-c7bd31a53817
Each app you create has it is own context, using the below block of code:
with app.app_context():
db.init_app(app)
means that you initialize those instances to that app context only and trying to access those instances somewhere else will result in the below error.
RunTimeError: Working outside of application context.
You can read more about Flask app context here
Related
I have created a Flask prediction app (within Google Colab) and when I am trying to run it post adding all the dependencies within the colab environment I am getting the url but when I click on it it show site cannot be reached.
I have the Procfile, the pickled model and the requirements text file but for some reason its not working. Also, I tried deploying this app using Heroku and it met the same fate where I got the app error.
For more context please visit my github repo.
Any help or guidance will be highly appreciated.
from flask import Flask, url_for, redirect, render_template, jsonify
from pycaret.classification import*
import pandas as pd
import numpy as np
import pickle
app = Flask(__name__)
model = load_model('Final RF Model 23JUL2021')
cols = ['AHT','NTT','Sentiment','Complaints','Repeats']
#app.route('/')
def home():
return render_template("home.html")
#app.route('/predict',methods=['POST'])
def predict():
int_features = [x for x in request.form.values()]
final = np.array(int_features)
data_unseen = pd.DataFrame([finak], columns = cols)
prediction = predict_model(model, data=data_unseen, round=0)
prediction = int(prediction.Label[0])
return render_template('home.html',pred='Predicted Maturiy Level is{}'.format(prediction))
#app.route('/predict_api',methods=['POST'])
def predict_api():
data = request.get_json(force=True)
data_unseen = pd.DataFrame([data])
prediction = predict_model(model, data=data_unseen)
output = prediction.Label[0]
return jsonify(output)
if __name__ == '__main__':
app.run(debug=True)
You cannot run flask app same as in your machine. You need to use flask-ngrok.
!pip install flask-ngrok
from flask_ngrok import run_with_ngrok
[...]
app = Flask(__name__)
run_with_ngrok(app)
[...]
app.run()
You can't use debug=True parameter in ngrok.
I would like to add data to a database with Flask-SQLAlchemy without the Flask app running.
Is there a way to get db back from the app after the app and the database have been initialized.
My code looks like
db = SQLAlchemy()
def init_app():
app = Flask(__name__)
db = SQLAlchemy(app)
db.init_app(app)
return app
And what I would like to do is something like
from app import init_app
app = init_app() # initialized but not running
# db is used in model.py, but not initialized
# with Flask
# from db = SQLAlchemy()
from model import Machine # class Machine(db.Model)
p = Machine(name='something')
# now I need the initialized db from somewhere
db.session.add(p)
db.session.commit()
Basically I would like to do what's described here:
Another disadvantage is that Flask-SQLAlchemy makes using the database
outside of a Flask context difficult. This is because, with
FLask-SQLAlchemy, the database connection, models, and app are all
located within the app.py file. Having models within the app file, we
have limited ability to interact with the database outside of the app.
This makes loading data outside of your app difficult. Additionally,
this makes it hard to retrieve data outside of the Flask context.
Well, once you initialize the app, Flask spines a server (either development or production, whichever you set), so if you would like to add data to a database with Flask-SQLAlchemy without the Flask app running, you would better use the flask shell command which runs in the context of the current app, then you could add your data.
But first, it would be better is you set up your app as the following so we could directly import stuff like db, auth, etc:
...
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
def init_app():
app = Flask(__name__)
db.init_app(app)
return app
In the root of your project, type in the terminal the following command
flask shell
Now that you have a shell running in the context of the current app but not the server not running:
from app import db
from model import Machine # class Machine(db.Model)
p = Machine(name='something')
# now I need the initialized db from somewhere
db.session.add(p)
db.session.commit()
From the wonderful tutorial...
https://blog.miguelgrinberg.com/post/the-flask-mega-tutorial-part-iv-database
Define something like this...
from app import app, db
from app.models import User, Post
#app.shell_context_processor
def make_shell_context():
return {'db': db, 'User': User, 'Post': Post}
And then...
(venv) $ flask shell
>>> db
<SQLAlchemy engine=sqlite:////Users/migu7781/Documents/dev/flask/microblog2/app.db>
>>> User
<class 'app.models.User'>
>>> Post
<class 'app.models.Post'>
I have the following structure:
app_dir/
| myapi/
| __init__.py
| myapi_app.py
where myapi_app.py is
from myapi import create_app, db
app = create_app()
and myapi/__init__.py is
import logging
import os
from logging.handlers import RotatingFileHandler
from flask import Flask, request, current_app
from flask_sqlalchemy import SQLAlchemy
from myapi.config import Config
db = SQLAlchemy()
def create_app(config_class=Config):
app = Flask(__name__)
app.config.from_object(config_class)
db.init_app(app)
...
return app
When I set FLASK_APP=myapi_app.py and run flask run from the app_dir directory, the flask service starts. However, when I make a request, I get the following error: flask.cli.NoAppException: Could not import "myapi_app". Where am I going wrong?
Your problem is that you are setting $FLASK_APP to the file in which the app variable is stored, you should instead set it to the python object path, e.g.
FLASK_APP=myapi_app:app
However, this is not necessary, as you could also just do:
FLASK_APP=myapi
as Flask will look for a create_app function in the package on its own.
I have a very small Flask app that is laid out as follows:
tinker/
main.py
/my_package
init.py
views.py
When I do tinker>python main.py everything runs fine. Here are the contents of each file:
main.py:
from my_package import app
app.run()
my_package/init.py:
from flask import Flask
app = Flask(__name__)
from my_package import views
my_package/views.py:
from my_package import app
#app.route('/')
def home():
return 'Ola!!!!!'
While all the above code runs fine when I try to modify it slightly by using a a create_app() code pattern, as in the below, views.py throws the following exception: "ImportError: cannot import name 'app' from 'my_package' " Is there a way to fix the problem without using Blueprints?
main.py:
from my_package import create_app
app = create_app()
app.run()
my_package/init.py:
from flask import Flask
def create_app():
app = Flask(__name__)
from my_package import views
return app
my_package/views.py:
from my_package import app
#app.route('/')
def home():
return 'Ola!!!!!'
You import the views within application context, then in the views you can use current_app.
in mypackage/__init__.py:
def create_app():
app = Flask(__name__)
with app.app_context():
from . import views
in mypackage/views.py:
from flask import current_app
#current_app.route('/')
def index():
return 'hello, world!'
init.py needs to be renamed to __init__.py
Move app = Flask(__name__) outside of the create_app method
Change to from . import app in views.py
This is Flask app context
app = Flask(__name__)
with app.app_context():
# insert code here
Most of the use cases of app context involves having 'app' initialized on the same script or importing app from the base.
My application is structured as the following:
# application/__init__.py
def create_app(config):
app = Flask(__name__)
return app
# manage.py
from application import create_app
from flask_script import Manager
manager = Manager(create_app)
manager.add_command("debug", Server(host='0.0.0.0', port=7777))
This might be really trivial issue, but how I should call 'with app.app_context()' if my application is structured like this?
Flask-Script calls everything inside the test context, so you can use current_app and other idioms:
The Manager runs the command inside a Flask test context. This means that you can access request-local proxies where appropriate, such as current_app, which may be used by extensions.
http://flask-script.readthedocs.org/en/latest/#accessing-local-proxies
So you don't need to use with app.app_context() with Manager scripts. If you're trying to do something else, then you'd have to create the app first:
from application import create_app
app = create_app()
with app.app_context():
# stuff here