Home » Python » Introduction to the Flask Python Web App Framework

About Bhagvan Kommadi

Bhagvan Kommadi is the Founder of Architect Corner & has around 20 years’ experience in the industry, ranging from large scale enterprise development to helping incubate software product start-ups. He has done Masters in Industrial Systems Engineering at Georgia Institute of Technology (1997) and Bachelors in Aerospace Engineering from Indian Institute of Technology, Madras (1993). He is member of IFX forum,Oracle JCP and participant in Java Community Process. He founded Quantica Computacao, the first quantum computing startup in India. Markets and Markets have positioned Quantica Computacao in ‘Emerging Companies’ section of Quantum Computing quadrants. Bhagvan has engineered and developed simulators and tools in the area of quantum technology using IBM Q, Microsoft Q# and Google QScript. He has reviewed the Manning book titled : "Machine Learning with TensorFlow”. He is also the author of Packt Publishing book - "Hands-On Data Structures and Algorithms with Go".He is member of IFX forum,Oracle JCP and participant in Java Community Process. He is member of the MIT Technology Review Global Panel.

Introduction to the Flask Python Web App Framework

This is an article about Flask Python Web App Framework.

1. Introduction

Flask is a popular open-source web framework. It is used for creating web applications in python. It was created by POCCO (International group of python enthusiasts) Lead Armin Ronacher.

2. Flask Web App Framework

Flask is a microframework based on the Jinja2 web template engine and WSGI toolkit. WSGI is a web server gateway interface. It is a web application development standard using python. It acts as an interface between the web app and the webserver. Jinja2 engine is used for adding web template for a dynamic web page.

2.1 Prerequisites

Python 3.6.8 is required on windows or any operating system. Pycharm is needed for python programming.

2.2 Download

Python 3.6.8 can be downloaded from the website. Pycharm is available at this link.

2.3 Setup

2.3.1 Python Setup

To install python, the download package or executable needs to be executed.

2.4 IDE

2.4.1 Pycharm Setup

Pycharm package or installable needs to be executed to install Pycharm.

2.5 Launching IDE

2.5.1 Pycharm

Launch the Pycharm and start creating a pure python project named HelloWorld. The screen shows the project creation.

flask python - Pycharm Create project
Pycharm Create project

The project settings are set in the next screen as shown below.

flask python - Pycharm Project Settings
Pycharm Project Settings

Pycharm welcome screen comes up shows the progress as indicated below.

flask python - project view
Pycharm Project View

You can create a Hello.py and execute the python file by selecting the Run menu.

flask python - hello world
Pycharm Hello World

The output message “Hello World” is printed when the python file is Run.

flask python - pycharm
Pycharm Python Execution

2.6 Flask configuration

 To configure Flask, you need to install virtualenv. Virtualenv is used for handling more than one python virtual environments.

The command below is used for installing virtualenv :

VirtualEnv installation
pip3 install virtual env

The output of the above commands is shown below:

Vrtual Env setup
apples-MacBook-Air:flask bhagvan.kommadi$ pip3 install virtualenv
Collecting virtualenv
  Downloading virtualenv-20.4.2-py2.py3-none-any.whl (7.2 MB)
     |████████████████████████████████| 7.2 MB 851 kB/s 
Collecting filelock=3.0.0
  Downloading filelock-3.0.12-py3-none-any.whl (7.6 kB)
Collecting distlib=0.3.1
  Downloading distlib-0.3.1-py2.py3-none-any.whl (335 kB)
     |████████████████████████████████| 335 kB 774 kB/s 
Requirement already satisfied: importlib-metadata>=0.12; python_version < "3.8" in /usr/local/lib/python3.7/site-packages (from virtualenv) (1.6.0)
Requirement already satisfied: six=1.9.0 in /usr/local/lib/python3.7/site-packages (from virtualenv) (1.15.0)
Requirement already satisfied: appdirs=1.4.3 in /usr/local/lib/python3.7/site-packages (from virtualenv) (1.4.4)
Requirement already satisfied: zipp>=0.5 in /usr/local/lib/python3.7/site-packages (from importlib-metadata>=0.12; python_version virtualenv) (3.1.0)
Installing collected packages: filelock, distlib, virtualenv
Successfully installed distlib-0.3.1 filelock-3.0.12 virtualenv-20.4.2
apples-MacBook-Air:flask bhagvan.kommadi$

The following commands are used for creation and activation of the environment:

VirtualEnv Creation & Activation
mdkir flask
cd flask
virtualenv flaskenv
source flaskenv/bin/activate

The output of the above commands is shown below:

Output
apples-MacBook-Air:flask bhagvan.kommadi$ mkdir flask
apples-MacBook-Air:flask bhagvan.kommadi$ cd flask
apples-MacBook-Air:flask bhagvan.kommadi$ virtualenv flaskenv
created virtual environment CPython3.7.7.final.0-64 in 3002ms
  creator CPython3Posix(dest=/Users/bhagvan.kommadi/Desktop/JavacodeGeeks/Code/flask/flask/flaskenv, clear=False, no_vcs_ignore=False, global=False)
  seeder FromAppData(download=False, pip=bundle, setuptools=bundle, wheel=bundle, via=copy, app_data_dir=/Users/bhagvan.kommadi/Library/Application Support/virtualenv)
    added seed packages: pip==21.0.1, setuptools==52.0.0, wheel==0.36.2
  activators BashActivator,CShellActivator,FishActivator,PowerShellActivator,PythonActivator,XonshActivator
apples-MacBook-Air:flask bhagvan.kommadi$ source flaskenv/bin/activate
(flaskenv) apples-MacBook-Air:flask bhagvan.kommadi$

Flask can be installed by using the command below:

Flask installation
pip3 install flask

The output of the above commands is shown below:

Flask installation Output
(flaskenv) apples-MacBook-Air:flask bhagvan.kommadi$ pip3 install flask
Collecting flask
  Downloading Flask-1.1.2-py2.py3-none-any.whl (94 kB)
     |████████████████████████████████| 94 kB 600 kB/s 
Collecting Jinja2>=2.10.1
  Downloading Jinja2-2.11.3-py2.py3-none-any.whl (125 kB)
     |████████████████████████████████| 125 kB 814 kB/s 
Collecting click>=5.1
  Downloading click-7.1.2-py2.py3-none-any.whl (82 kB)
     |████████████████████████████████| 82 kB 654 kB/s 
Collecting Werkzeug>=0.15
  Downloading Werkzeug-1.0.1-py2.py3-none-any.whl (298 kB)
     |████████████████████████████████| 298 kB 762 kB/s 
Collecting itsdangerous>=0.24
  Downloading itsdangerous-1.1.0-py2.py3-none-any.whl (16 kB)
Collecting MarkupSafe>=0.23
  Downloading MarkupSafe-1.1.1-cp37-cp37m-macosx_10_9_x86_64.whl (16 kB)
Installing collected packages: MarkupSafe, Werkzeug, Jinja2, itsdangerous, click, flask
Successfully installed Jinja2-2.11.3 MarkupSafe-1.1.1 Werkzeug-1.0.1 click-7.1.2 flask-1.1.2 itsdangerous-1.1.0
(flaskenv) apples-MacBook-Air:flask bhagvan.kommadi$

Using Flask framework, you can build web application. The code below shows an example in Flask.

Flask example
from flask import Flask  
  
app = Flask(__name__)    
 
@app.route('/')    
def home():  
    return "Running Flask example";  
  
if __name__ =='__main__':  
    app.run(debug = True) 

The command below executes the above code snippet:

Flask example
python3 flaskexample.py

The output of the executed command is shown below.

Flask example
(flaskenv) apples-MacBook-Air:flask bhagvan.kommadi$ python3 flaskexample.py 
 * Serving Flask app "flaskexample" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: on
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
 * Restarting with stat
 * Debugger is active!
 * Debugger PIN: 981-329-817

You can access the web application at http://localhost:5000. The snapshot below shows the web application in the web browser.

flask python example
Flask Example

2.7 Connecting the database in Flask

You can use SQLite3 python module to develop web applications with database.

An example creating customers database is shown below in the code :

Customers Database
import sqlite3  
  
con = sqlite3.connect("customers.db")  
print("Customers Database opening")  
  
con.execute("create table Customers (customerid INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT NOT NULL, email TEXT UNIQUE NOT NULL, address TEXT NOT NULL)")  
  
print("Customer Table created successfully")  
  
con.close()  

The command below executes the above code snippet:

Customers Database
python3 CustomerData.py

The output of the executed command is shown below.

Creating Customers Database
(flaskenv) apples-MacBook-Air:flask bhagvan.kommadi$ python3 CustomerData.py
Customers Database opening
Customer Table created successfully
(flaskenv) apples-MacBook-Air:flask bhagvan.kommadi$ ls
CustomerData.py	customers.db	flaskenv	flaskexample.py
(flaskenv) apples-MacBook-Air:flask bhagvan.kommadi$

You can create an web application for adding customer records and viewing customer records. The code below shows the web application.

Customers Script
from flask import *  
import sqlite3  
  
app = Flask(__name__)  
 
@app.route("/")  
def index():  
    return render_template("index.html");  
 
@app.route("/add")  
def add():  
    return render_template("addCustomer.html")  
 
@app.route("/savedetails",methods = ["POST","GET"])  
def saveDetails():  
    msg = "msg"  
    if request.method == "POST":  
        try:  
            name = request.form["name"]  
            email = request.form["email"]  
            address = request.form["address"]  
            with sqlite3.connect("customers.db") as con:  
                cur = con.cursor()  
                cur.execute("INSERT into Customers (name, email, address) values (?,?,?)",(name,email,address))  
                con.commit()  
                msg = "Customer successfully Added"  
        except:  
            con.rollback()  
            msg = "We can not add the Customer to the list"  
        finally:  
            return render_template("success.html",msg = msg)  
            con.close()  
 
@app.route("/view")  
def view():  
    con = sqlite3.connect("customers.db")  
    con.row_factory = sqlite3.Row  
    cur = con.cursor()  
    cur.execute("select * from Customers")  
    rows = cur.fetchall()  
    return render_template("viewCustomer.html",rows = rows) 

The web pages referred in the code above are in the templates folder. The command below executes the above code snippet:

CRM Web application
python3 Customer.py

The output of the executed command is shown below.

Running CRM Webapp
(flaskenv) apples-MacBook-Air:flask bhagvan.kommadi$ python3 Customer.py
 * Serving Flask app "Customer" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: on
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
 * Restarting with stat
 * Debugger is active!
 * Debugger PIN: 981-329-817

You can check http://localhost:5000 on your browser. The images below the web pages.

CRM Web application

You can click on Add Customer to add customer

Add Customer Details

The output of the above form submission is shown below:

Customer Added

You can click on View Customers to see the records.

View Customers

2.8 Defining objects in Flask

In flask, Flask object implements a WSGI application. It is used for the name of the module or application package. Flask Object is the central registry for views, URL, rules, templates, and their configuration. Model object is extended by new Database objects. Flask SQLAlchemy package is used for modelling the relationships. Each database object will have attributes and relationships.

2.9 Model relationships

You can use the SQL Alchemy python module for using relational databases and modeling data-intensive web applications. In 2005, SQLAlchemy was developed by Mike Bayer. It has support for databases such as MySQL, PostgreSQL, Oracle, MS-SQL, SQLite, and others. It has an ORM mapper and you can use object-oriented code instead of raw SQL. Flask SQLAlchemy python extension has methods to use SQL Alchemy

The command used for installing flask SQLAlchemy is shown below:

Customers Database
pip3 install flask-sqlalchemy

To use different databases, the configuration examples are shown below:

Customers Database
# database URI for MySQL using PyMysql driver 'mysql+pymysql://root:pass@localhost/my_db' 
# database URI for PostgreSQL using psycopg2 'postgresql+psycopg2://root:pass@localhost/my_db'
 # database URI for MS-SQL using pyodbc driver 'mssql+pyodbc://root:pass@localhost/my_db'
 # database URI for Oracle using cx_Oracle driver 'oracle+cx_oracle://root:pass@localhost/my_db'

Model is a class for database table which inherits from db.Model. You can create a Author class as shown below:

Authors Model
class Author(db.Model):
   id = db.Column('author_id', db.Integer, primary_key = True)
   name = db.Column(db.String(100))
   city = db.Column(db.String(50))  
   addr = db.Column(db.String(200))
   pin = db.Column(db.String(10))

def __init__(self, name, city, addr,pin):
   self.name = name
   self.city = city
   self.addr = addr
   self.pin = pin

To model complex relationships, let us start off with one to one relationship. Author has Identity information. The code below shows the one to one relationship.

Author and Identity
class Author(db.Model):
   __tablename__ = 'authors'
   id = db.Column('author_id', db.Integer, primary_key = True)
   name = db.Column(db.String(100))
   city = db.Column(db.String(50))  
   addr = db.Column(db.String(200))
   pin = db.Column(db.String(10))
class Identity(db.Model):
    __tablename__ = 'identity'
    id = db.Column(db.Integer(), primary_key=True)
    license_number = db.Column(db.String(255), nullable=False)
    renewed_on = db.Column(db.Date(), nullable=False)
    expiry_date = db.Column(db.Date(), nullable=False)
    author_id = db.Column(db.Integer(), db.ForeignKey('authors.id'))

Let us see now, one to many relationship. You can create Hashtag and Article models as shown in the code below:

HashTag and Article
class Category(db.Model):
    __tablename__ = 'categories'
    id = db.Column('id', db.Integer, primary_key = True)
    created_on = db.Column(db.DateTime(), default=datetime.utcnow)
    articles = db.relationship('Article', backref='Category')

class Article(db.Model):
    __tablename__ = 'articles'
      id = db.Column('id', db.Integer, primary_key = True)
    updated_on = db.Column(db.DateTime(), default=datetime.utcnow, onupdate=datetime.utcnow)
    category_id = db.Column(db.Integer(), db.ForeignKey('categories.id'))

You can model many to many by adding hashtags to category and articles. The code below shows the modelling.

HashTag and Article
class Category(db.Model):
    __tablename__ = 'categories'
    id = db.Column('id', db.Integer, primary_key = True)
    created_on = db.Column(db.DateTime(), default=datetime.utcnow)
    article_hastags = db.Table('article_hashtags',
    db.Column('article_id', db.Integer, db.ForeignKey('articles.id')),
    db.Column('hashtag_id', db.Integer, db.ForeignKey('hashtags.id'))
)
    
class Hashtag(db.Model):
    __tablename__ = 'hashtags'
    id = db.Column('id', db.Integer, primary_key = True)
    created_on = db.Column(db.DateTime(), default=datetime.utcnow)
    articles = db.relationship('Article', backref='Hashtag')

class Article(db.Model):
    __tablename__ = 'articles'
      id = db.Column('id', db.Integer, primary_key = True)
    updated_on = db.Column(db.DateTime(), default=datetime.utcnow, onupdate=datetime.utcnow)
    category_id = db.Column(db.Integer(), db.ForeignKey('hashtags.id'))

2.10 Initializing the database

You need flask migrate package for database initialization. The command for installing flask migrate is as below:

Customers Database
pip3 install flask-migrate

You can create database initialization for our CRM application

Customers Database
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///customers.db'

db = SQLAlchemy(app)
migrate = Migrate(app, db)

class Customer(db.Model):
    customerid = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(128))
    email = db.Column(db.String(128))
    address = db.Column(db.String(128))

You can create a migration repository with command below:

Customers Database
flask db init

You can generate the first migration using the below command :

Customers Database
flask db migrate -m "Initial migration."

You can add this to your version control and apply when needed using the command below:

Customers Database
flask db upgrade

2.11 Flask requests

Flask python library has a request object which can be subclassed. It is a subclass of Request. The request object is used for sending data from the source to the destination. HTTP methods are used for accessing the data on the server-side. The request object has attributes such as Form, args, Cookies, files, and method. The requests package has methods for creating HTTP requests in python. It has features to handle validating headers and JSON serialization. This library helps in verifying the SSL Certificate. requests library has features such as max_retries, timeout,

4. Download the Source Code

Download
You can download the full source code of this example here: Introduction to the Flask Python Web App Framework

Last updated on May 31st, 2021

Do you want to know how to develop your skillset to become a Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you our best selling eBooks for FREE!

 

1. JPA Mini Book

2. JVM Troubleshooting Guide

3. JUnit Tutorial for Unit Testing

4. Java Annotations Tutorial

5. Java Interview Questions

6. Spring Interview Questions

7. Android UI Design

 

and many more ....

 

Receive Java & Developer job alerts in your Area

 

Subscribe
Notify of
guest

This site uses Akismet to reduce spam. Learn how your comment data is processed.

0 Comments
Inline Feedbacks
View all comments