Python Flask username availability check with MySQL, AJAX

Last Updated on May 19th, 2020 at 06:17 am


This tutorial shows an example on Python Flask username availability check with MySQL, AJAX. Sometimes we need to check username availability instantly before a user submits the form after filling a lengthy signup form.

In this case we can use AJAX with any technologies like PHP, Codeigniter, Servlet, Struts, JSF, Spring etc. for checking whether the input username is available or already occupied by someone else.

So if we give instant result to the user for username availability then sometimes it makes more sensible than while pressing the submit button and goes top of the signup form to rectify the username input field if input username is not available.

You may also read:

We will use here REST API on server side to check the username availability using Python Flask with MySQL and AJAX.


Python 3.7.4, Flask 1.1.1, MySQL 8.0.17, Windows 10 64 bit

Creating Project Directory

First step is to create a project root directory under which we will put all our required files for the project.

Let’s say I am going to create a project root directory python-flask-mysql-ajax-username-availability-check.

We may not mention the project root directory in subsequent sections and we will assume that we are talking with respect to the project’s root directory.

Creating MySQL Table

Create a table user under database roytuts in MySQL server with the following structure:

	`user_id` int unsigned NOT NULL AUTO_INCREMENT,
	`login_username` varchar(100) NOT NULL,
	`login_password` varchar(255) NOT NULL,
	`last_login` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
	PRIMARY KEY (`user_id`),
	UNIQUE KEY `login_email_UNIQUE` (`login_username`)

Dumping Data

We need to insert some data in order to complete the test that checks whether the functionality is really working as expected.

insert into `user`(`user_id`,`login_username`,`login_password`,`last_login`) 
values (1,'user1','$2a$08$S5IfrpOVOvFbbOSOmZpjsO5N9PXgEerTloK','2014-07-19 19:18:30'),(2,'user2','$2a$08$v1kJflweCK3FOcoAsmYAUCMxFa5Shh7c2','2013-11-17 19:22:46');

Configuring Flask

Create the below script(py is the extension to indicate Python script) where we import the flask module. This file should be created under the project root directory. Notice how we create flask instance. We don’t need to configure secret key because we are not going to use flash or session in our application.

from flask import Flask

app = Flask(__name__)

Database Configuration

We create the below Python script under project root directory to setup the MySQL database configurations for connecting to database.

We need to configure database connection with flask module and that’s why we have imported app module and setup the MySQL configuration with flask module.

from app import app
from flaskext.mysql import MySQL

mysql = MySQL()
# MySQL configurations
app.config['MYSQL_DATABASE_USER'] = 'root'
app.config['MYSQL_DATABASE_PASSWORD'] = 'root'
app.config['MYSQL_DATABASE_DB'] = 'roytuts'
app.config['MYSQL_DATABASE_HOST'] = 'localhost'

Configuring URLs

Next we will create script that will define all URIs or Action paths for checking user information into the database.

In this script we will use view as well as REST API endpoint.

The view will display the home page template with input form where user will input username.

The REST API endpoint will give us access to check username availability instantly with AJAX and jQuery oninput event.

We first import required modules into the script. We then define the end-point / for displaying a view where user will see the home page with input form.

Next we need to validate user input data and verify the input username exists or not in the database. So we define another REST end-point /user_check.

We use http method GET for displaying view and POST method for sending data to server side.

By default http method is GET if you do not specify http method.

We use render_template function from flask to show the view.

import pymysql
from app import app
from db_config import mysql
from flask import jsonify, request, render_template
@app.route('/user_check', methods=['POST'])
def username_check():
	conn = None
	cursor = None
		username = request.form['username']
		# validate the received values
		if username and request.method == 'POST':		
			conn = mysql.connect()
			cursor = conn.cursor(pymysql.cursors.DictCursor)
			cursor.execute("SELECT * FROM user WHERE login_username=%s", username)
			row = cursor.fetchone()
			if row:
				resp = jsonify('<span style=\'color:red;\'>Username unavailable</span>')
				resp.status_code = 200
				return resp
				resp = jsonify('<span style=\'color:green;\'>Username available</span>')
				resp.status_code = 200
				return resp
			resp = jsonify('<span style=\'color:red;\'>Username is required field.</span>')
			resp.status_code = 200
			return resp
	except Exception as e:
def home():
	return render_template('username.html')
if __name__ == "__main__":

View – Template File

Create a templates directory under the project’s root directory and create a template file username.html with the below content.

Now we will create a form where user will input username and check whether the given username is available or not.

We will use here jQuery’s on function with input event to check username live.

We will use jQuery libraries directly from the CDN.

<!DOCTYPE html>
	<meta charset="UTF-8">
	<title>Check username availability using Python Flask, AJAX, MySQL</title>
	<script src=""></script>
	<script src=""></script>
	<script src=""></script>
	<div style="margin: 10px 0 0 10px;width: 600px">
		<h3>Python Flask, AJAX, MySQL - username availability check</h3>
		<form id="signupform" style="padding: 10px;">
				<legend>Check username</legend>
					<input type="text" name="username" id="username" autocomplete="off"/>
					<div id="msg"></div>

	<!-- below jquery code triggered on onblur event and checks the username availability in the database -->
	<script type="text/javascript">
		$(document).ready(function() {
			$("#username").on('input', function(e) {
				if ($('#username').val() == null || $('#username').val() == "") {
					$("#msg").html("Username is required field.").css("color", "red");
				} else {
						type: "POST",
						url: "http://localhost:5000/user_check",
						data: $('#signupform').serialize(),
						dataType: "html",
						cache: false,
						success: function(msg) {
						error: function(jqXHR, textStatus, errorThrown) {
							$("#msg").html(textStatus + " " + errorThrown);

Testing the Application

Now navigate to the project’s root directory and execute the command python as shown in the below image, your server will start on default port 5000.

If you want to change the port then you can change the line to, where 5001 is the new port.

Hit the URL http://localhost:5000 to open the home page and you will see below output on the page:

python flask username availability check with mysql ajax

Now you can input and check whether username is available or not. You will see the instance result while you type a letter or on key up.

Source Code

download source code

Thanks for reading.

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