Flask Cheatsheet

Published December 26, 2021

What is Flask

Flask is a micro web framework written in Python. It is classified as a microframework because it does not require particular tools or libraries. It has no database abstraction layer, form validation, or any other components where pre-existing third-party libraries provide common functions.

Importing Flask

from flask import Flask

Most used import functions

These are some of the most used import functions

from flask import Flask, render_template, redirect, url_for, request

Boilerplate

This is the basic template or barebone structure of Flask.

from flask import Flask
    
app = Flask(__name__)
    
 @app.route("/")
    def hello_world():
    return "<p>Hello, World!</p>"
    
    app.run()

route(endpoint)

This is to make different endpoints in our flask app.

@app.route("/")

Route method

Allowing get and post requests on an endpoint.

methods = ['GET', 'POST']

Re-run while coding

This is used to automatically rerun the program when the file is saved.

app.run(debug=True)

Change host

This is used to change the host.

app.run(host='0.0.0.0')

Change port

This is used to change the port.

app.run(port=80)

SQLAlchemy

from flask_sqlalchemy import SQLAlchemy

Database URI

This is the database's address.

app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://username:password@localhost/db_name' 
    or 
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:/Initialization
This is used to initialize SQLAlchemy.
db = SQLAlchemy(app)
 
Creating Model
Class to get data from database and to send data to the database.
class TableName(db.Model): 
        column_1 = db.Column(db.Integer, primary_key=True) 
        column_2 = db.Column(db.String(80), nullable=False) 
        column_3 = db.Column(db.String(12), nullable=False)
Get all data(.all())
This is used to get all the data from the database.
data = ClassName.query.filter_by().all()
Filtered data(.first())
This is used to get the first dataset from the list returned by the filter_by function. You can get targetted data by this.
data = ClassName.query.filter_by().first()
Send/add data to database
This is used to send/add data to the database.
data_to_send = ClassName(column_1=dataset1, column_2=dataset2, column_3=dataset3) 
        db.session.add(data_to_send) 
        db.session.commit()
Delete data from the database
This is used to delete data from the database.
data_to_send = ClassName(column_1=dataset1, column_2=dataset2, column_3=dataset3)
        db.session.delete(data_to_send)
        db.session.commit()
Request method
This is used to know what request is made(get/post).
request.method
Render Template
This is used to pass whole html file directly.
render_template("file.html")
FSADeprecationWarning
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True|False
Creating Database file
This is used to create a database file
from yourapplicationname import db 
        db.create_all() 
        exit()
Method to return database items
This is used to return database items.
def __repr__(self) -> str: 
        return f"{self.item}"
Printing returned content from the method
This is used to print returned database items.
data = ClassNameWithMethod.query.all() 
        print(data)
Flask Documentation
https://flask.palletsprojects.com/en/latest/
Flask SQLAlchemy Documentation
https://flask-sqlalchemy.palletsprojects.com/en/2.x/
//test.db'

Initialization

This is used to initialize SQLAlchemy.

db = SQLAlchemy(app)

Creating Model

Class to get data from database and to send data to the database.

class TableName(db.Model): 
    column_1 = db.Column(db.Integer, primary_key=True) 
    column_2 = db.Column(db.String(80), nullable=False) 
    column_3 = db.Column(db.String(12), nullable=False)

Get all data(.all())

This is used to get all the data from the database.

data = ClassName.query.filter_by().all()

Filtered data(.first())

This is used to get the first dataset from the list returned by the filter_by function. You can get targetted data by this.

data = ClassName.query.filter_by().first()

Send/add data to database

This is used to send/add data to the database.

data_to_send = ClassName(column_1=dataset1, column_2=dataset2, column_3=dataset3) 
    db.session.add(data_to_send) 
    db.session.commit()

Delete data from the database

This is used to delete data from the database.

data_to_send = ClassName(column_1=dataset1, column_2=dataset2, column_3=dataset3)
    db.session.delete(data_to_send)
    db.session.commit()

Request method

This is used to know what request is made(get/post).

request.method

Render Template

This is used to pass whole html file directly.

render_template("file.html")

FSADeprecationWarning

app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True|False

Creating Database file

This is used to create a database file

from yourapplicationname import db 
    db.create_all() 
    exit()

Method to return database items

This is used to return database items.

def __repr__(self) -> str: 
    return f"{self.item}"

Printing returned content from the method

This is used to print returned database items.

data = ClassNameWithMethod.query.all() 
    print(data)

Flask Documentation

https://flask.palletsprojects.com/en/latest/

Flask SQLAlchemy Documentation

https://flask-sqlalchemy.palletsprojects.com/en/2.x/