If you are not familiar with SQLAlchemy, check out my article Getting Started with SQLAlchemy.

Flask uses the MVC (Model View Controller) Framework. Just to make this as obvious as possible, I like my Flask apps to have the following.

• Model -> models.py
• View -> views.py
• Controller -> __init__.py

And let's say your Flask app has the following structure.

├── main.py
├── database (directory)
│   ├── example.db
├── my-project (directory)
│   ├── __init__.py
│   ├── views.py
│   ├── models.py
│   ├── templates (directory)
│   │   ├── base.html
│   │   ├── home.html
│   │   ├── results.html
│   └── static (directory)
│       └── custom.css

You will need to install the psycopg module to be able to make the connection to Postgres.

pip install flask-sqlalchemy
pip install psycopg2

Or, you can specify the version to install

pip install flask-sqlalchemy==3.0.5
pip install psycopg2==2.9.6

Or, better yet, use a requirements.txt file.

flask-sqlalchemy==3.0.5
psycopg2==2.9.6

And then install the packages using the requirements.txt file.

pip install --requirement requirements.txt

create_engine(uri) can be used to make the connection to Postgres. In this example, create_engine(uri) is in __init__.py.

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import create_engine

db = SQLAlchemy()

def app_obj():
    app = Flask(__name__)
    uri = 'postgresql+psycopg2://johndoe:itsasecret@10.21.50.198:5432/mydb'
    app.config['SQLALCHEMY_DATABASE_URI'] = uri
    app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
    db.init_app(app)

    with app.app_context():
        db.create_engine(uri)

    return app

And then your view, such as views.py, engine.connect() can be used to test the connection to Postgres.

from flask import Blueprint
from . import app, db
from sqlalchemy import exc

views = Blueprint('views', __name__)

@views.route('/')
def home():
    try:
        db.engine.connect()
    except exc.SQLAlchemyError as sqlalchemyerror:
        return sqlalchemyerror
    except Exception as exception:
        return exception
    else:
        return "no exceptions were raised - it appears the connection to Postgres was successful"