Paint Application Using Flask and Sqlite3

     Now, I have rewritten the paint application in Google AppEngine using Flask framework.The html frontend and javascript are same.Please refer my earlier post about paint application for more info.Instead of google datastore, sqlite3 was used for data storage.I will explain how to connect to database and retrive data from it.

def connect_db():
    return sqlite3.connect('paint.db')

@app.before_request
def before_request():
    g.db = connect_db()
    g.db.execute("CREATE TABLE IF NOT EXISTS drawings(fname string primary key, img_data text)")
@app.after_request
def after_request(response):
    g.db.close()
    return response

First we define a function 'connect_db()' for connecting to database before requesting.Then create a table in database file(paint.db) for storing fname and img_data.

@app.route('/', methods=['GET', 'POST'])
def paint():
    if request.method == 'GET':
        py_all = {}
        all_data = g.db.execute("SELECT * FROM drawings")
        for data in all_data:
            py_all[data[0]] = data[1]
        return render_template('paint.html', py_all= py_all)
    elif request.method == 'POST':
        filename = request.form['fname']
        data = request.form['whole_data']
        g.db.execute("REPLACE INTO drawings(fname, img_data) VALUES (?, ?)", (filename, data));
        g.db.commit()
        return redirect('/')

          In GET method the data executed from database is render to  paint.html file.The data taken from data base is stored in 'py_all' object.When user tries to save the image, server gets a POST request.  the image name and its data are saved into a table using the sqlite3 module available in python. Sqlite3 is a basic database interface available in python.
The code can be found Here

Flask

      Flask is a lightweight web application framework written in Python. Flask is called a microframework because it keeps the core simple but extensible. Helps both for development and deployment of web applications. Flask depends on two external libraries, Werkzeug and Jinja2. Werkzeug is a toolkit for WSGI, the standard Python interface between web applications and a variety of servers for both development and deployment. Jinja2 renders templates. Flask application can test in local machine by using local server. Then finally you can deploy it on web server.This post gives a good introduction to Flask.

Installation:

Install flask in your local machine using the command:

sudo apt-get install python-flask

Simple App: Hello world

simple Flask application looks like this:

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello World!'

if __name__ == '__main__':
    app.run() 

In this code first we imported the flask class.first argument is the name of the application's module.if you are using single module, you should use __name__. Next we create an instance of this class. we pass it the name of module. This is needed so that Flask knows where to look for templates, static files and soon. Then route() decorator is used to bind a function to URL

Just save it as hello.py and run with your Python interpreter. The local server is now running

$ python hello.py
    * Running on http://127.0.0.1:5000/

You should see your hello world message on http://127.0.0.1:5000/
To stop the server, use Control-C

STUDENTS APPLICATION IN FLASK

In this tutorial  we will create a simple web application 'student details'. The student details application provide you entering details of students and get back all data by sorting order by age and mark, also provide remove option and search option. We will use Flask and SQLite database with Python.

 Creating Folders

Before we get started, let’s create the folders needed for this application where we drop our files:

/students-app

       /static

       /templates