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NameError: name 'app' is not defined In Python

I am new to flask and i have been struggling to create an sqlite database but whenever i run the from app import db I get the error message:
NameError: name 'app' is not defined
This is my code:
from flask import Flask, render_template
from flask_sqlalchemy import SQLAlchemy
from datetime import datetime
app = Flask(__name__)
db = SQLAlchemy()
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db'
db.init_app(app)
class Todo:
id = db.Column(db.Integer(), primary_key=True)
content = db.Column(db.String(length=300), nullable=False)
date_created = db.Column(db.DateTime, default=datetime.utcnow)
def __repr__(self):
return '<Task %r>' % self.id
#app.route('/')
def index():
return render_template('index.html')
if __name__ == "__main__":
app.run(debug=True)`
The image below is my directory structure. I don't know if it has anything to do with it: Image of directory structure
I tried import db from app so that I will create the db file.

First u need to replace db.init_app(app) with db = SQLAlchemy(app). The starting code could look like this:
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db'
db = SQLAlchemy(app)
Then after your class Todo:
with app.app_context():
db.create_all()

Python Flask Postgres error - Can't generate DDL for NullType(); did you forget to specify a type on this Column?

Seemingly out of the blue I started getting this error whenever I try to run my flask app.
Can't generate DDL for NullType(); did you forget to specify a type on this Column?
I've changed nothing with the code or database. It runs fine from another server so I'm thinking it has to be something with the computer I'm running the script on but I'm out of ideas. I restarted my computer, restarted the database. Here is the code
from flask import Flask, jsonify
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://postgres:password#ngdeva-2/flaskapp2'
db = SQLAlchemy(app)
class Project(db.Model):
id = db.Column(db.Integer, primary_key=True)
wmx_jobid = db.Column(db.String(120), unique=True, nullable=False)
def __repr__(self):
return f"{self.id} - {self.wmx_jobid}"
db.create_all()
#app.route('/', methods=['GET'])
def home():
message = 'Flask is UP and RUNNING!'
return jsonify(message)
if __name__ == "__main__":
from waitress import serve
serve(app, host="0.0.0.0", port=8080)

Something must have been jacked up with my Python venv. I deleted/recreated the venv and that fixed the problem.

Flask throwing exception when i run my app

I started a simple Flask project, i'm using SLQAlchemy to handle my Database. My problem is that every time i run my app, i'll get the following error:
File "C:\Users\user\AppData\Local\Programs\Python\Python38\lib\site-packages\flask_sqlalchemy\__init__.py", line 137, in __init__
track_modifications = app.config['SQLALCHEMY_TRACK_MODIFICATIONS']
KeyError: 'SQLALCHEMY_TRACK_MODIFICATIONS'
Here is my code:
from flask import Flask, request, jsonify
import json
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import Column, Integer, String
from sqlalchemy.schema import FetchedValue
app = Flask(__name__)
db = SQLAlchemy()
class User(db.Model):
__tablename__ = 'users'
__table_args__ = {'schema': 'tvtg'}
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(350), nullable=False)
email = db.Column(db.String(350), nullable=False)
password = db.Column(db.String(350), nullable=False)
#app.route('/')
def hello_world():
print('HERE')
peter = User.query.filter_by(name='peter').first()
print(peter)
return 'hello_world'
if __name__ == "__main__":
app.run()
Can anyone help me find what i'm doing wrong? The traceback of the error is not helping me much

Actually, it looks like when using flask-sqlalchemy, you have to set a value for SQLALCHEMY_TRACK_MODIFICATIONS - even the documentation says otherwise (defaults to None).
Whether you want to set it to True or False is up to your use case, see documentation
https://flask-sqlalchemy.palletsprojects.com/en/2.x/config/
Or have a look at this great tutorial
https://blog.miguelgrinberg.com/post/the-flask-mega-tutorial-part-iv-database
The unreleased Flask-Sqlalchemy version 3 sets a new default of False.

Creating database via flask in postgreSQL

I m trying a tutorial, to make a database connection with flask, and postgreSQL database using json.
This is the code lines in models.py
from app import db
from sqlalchemy.dialects.postgresql import JSON
class Result(db.Model):
_tablename_= 'results'
id =db.Column(db.Integer, primary_key=True)
url = db.Column(db.String())
result_all = db.Column(JSON)
result_no_stop_words = db.Column(JSON)
def __init__(self, url, result_all, result_no_stop_words):
self.url = url
self.result_all = result_all
self.result_no_stop_words = result_no_stop_words
def __repr__(self):
return '<id {}>'.format(self.id)
Code in config.py
import os
basedir = os.path.abspath(os.path.dirname(__file__))
class Config(object):
DEBUG = False
TESTING = False
CSRF_ENABLED = True
SECRET_KEY = 'this-really-needs-to-be-changed'
SQLALCHEMY_DATABASE_URI = os.environ['postgresql://postgresql:bat123#localhost/DatabaseFirst']
class ProductionConfig(Config):
DEBUG = False
class StagingConfig(Config):
DEVELOPMENT = True
DEBUG = True
class DevelopmentConfig(Config):
DEVELOPMENT = True
DEBUG = True
class TestingConfig(Config):
TESTING = True
Code in manage.py
import os
from flask_script import Manager
from flask_migrate import Migrate, MigrateCommand
from app import app, db
app.config.from_object(os.environ['APP_SETTINGS'])
migrate = Migrate(app, db)
manager = Manager(app)
manager.add_command('db', MigrateCommand)
if __name__ == '__main__':
manager.run()
code in app.py
from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy
import os
app = Flask(__name__)
app.config.from_object(os.environ['APP_SETTINGS'])
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
db = SQLAlchemy(app)
from models import Result
#app.route('/')
def hello():
return "Hello World!"
#app.route('/<name>')
def hello_name(name):
return "Hello {}!".format(name)
if __name__ == "__main__":
app.run()
I want to know before running this code lines should the database be created in postgreSQL, alone with the table, and columns,
Or these code lines creating the table, and columns in postgreSQL
class Result(db.Model):
_tablename_= 'results'
id =db.Column(db.Integer, primary_key=True)
url = db.Column(db.String())
result_all = db.Column(JSON)
result_no_stop_words = db.Column(JSON)
Basically i want to know the function or purpose served by the above set of code lines.(5 code lines)

manager.add_command('db', MigrateCommand) this piece adds a command called db so that you can run flask db which will create the tables and columns.
Note: inorder to use this command first you need to define FLASK_APP in the environment variables.
Eg:
export FLASK_APP=app.py
flask db
Also the model
class Result(db.Model): _tablename_= 'results' id =db.Column(db.Integer, primary_key=True) url = db.Column(db.String()) result_all = db.Column(JSON) result_no_stop_words = db.Column(JSON)
This defines the class representation of the table. It won't create table in database, it's just the representation. The MigrationCommand is responsible for the creation of tables in database.

class Result(db.Model):
__tablename__ = 'results'
id =db.Column(db.Integer, primary_key=True)
class Result(db.Model):
This code line is creating a class instance of Result in front end of Flask application and to pass those values to the Database postgreSQL or whatever respective database you will be using.
__tablename__ = 'results':
Here we are creating a table called results in the database in my case DatabaseFirst
id = db.Column(db.Integer, primary_key=True):
Here we are creating a column called id, in our table called results, which can hold only data of integer type and id column is assigned the primary key of the results table.
Here by the 3 code lines I mentioned above, the database tables and columns are created via the Flask application, and we can see the respective results on postgreSQL database.

Why does my database get reset after each deployment?

I am new to deploying to aws as well as flask. Basically I have a simple Flask app but every time I make a change and deploy the new code to aws elastic beanstalk, the db gets reset.
from dateutil import parser
from datetime import datetime
from flask import Flask, request, jsonify
from flask_sqlalchemy import SQLAlchemy
from flask_marshmallow import Marshmallow
from flask_cors import CORS
import os
application = app = Flask(__name__)
basedir = os.path.abspath(os.path.dirname(__file__))
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///' + os.path.join(basedir, 'db.sqlite')
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True
db = SQLAlchemy(app)
ma = Marshmallow(app)
cors = CORS(app)
#app.route('/')
def hello():
return 'hello'
.
.
.
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String)
weight = db.Column(db.Float)
workouts = db.relationship('Workout', backref='user', lazy=True)
def __init__(self, name, weight):
self.name = name
self.weight = weight
class UserSchema(ma.Schema):
class Meta:
fields = ('id', 'name', 'weight')
user_schema = UserSchema(strict=True)
users_schema = UserSchema(many=True, strict=True)
.
.
.
db.create_all()
if __name__ == '__main__':
app.run(debug=True)
I expect that each time I
eb deploy flask-env my db wouldnt get reset but it does. For instance if i create a user and then later change something in the code and deploy, that user is gone.

You should:
Create an EBS Volume
Load the database into that volume
Attach the EBS Volume to your Beanstalk app with an .ebextension. An example can be found here.
With all that being said, this is not a highly available, well architected solution and will deteriorate at scale rapidly.
You will want to replace SQLite with an RDS instance at some point in the future before it becomes a problem.