Flask - Part 4


This version_4 will show you how to create signup and login routes.

Setting up

To begin we will start from our previous version_3 app. If you don’t have it anymore, no worries, simply copy the reference code :

# assuming you're in flask_learning
cp -R flask_cybermooc/version_3 my_app_v4
cd my_app_v4

and initialize our venv :

# assuming you're in flask_learning/my_app_v4
virtualenv venv -p python3
source venv/bin/activate
# (venv)
pip install -r requirements.txt # install from the requirements.txt file

All set up ? let’s begin.

1 - Bcrypt

Because we will store passwords, we need to store them properly. (no md5 is not a proper way to store password). We will use the bcrypt algorithm.

1.1 - Installing bcrypt

In our venv, let’s install flask-bcrypt which contains bcrypt + a wrapper for flask.

And we don’t forget to update our requirements.txt.

# assuming you're in flask_learning/my_app_v4 (venv)
pip install flask-bcrypt
pip freeze > requirements.txt

1.2 - Adding bcrypt to our app

Now that bcrypt is installed, we need to tell our app to use bcrypt when it starts.

It’s a good idea to keep the Marshmallow object instance in a separate file, to avoid circular imports.

To do so, let’s create the marshmallow file :

# assuming you're in flask_learning/my_app_v4 (venv)
touch app/bcrypt.py

and add this code :

# bcrypt.py

from flask_bcrypt import Bcrypt

bc = Bcrypt()

In the application_factory __init__.py, let’s update our code :

# app/__init__.py

from flask import Flask

def create_app():
    app = Flask(__name__)
    from os import environ as env
    app.config['SQLALCHEMY_DATABASE_URI'] = env.get('DATABASE_URL')

    from .database import db

    from .bcrypt import bc

    from .cli import cli_init_app

    from .api_v1 import api_v1_blueprint, root_blueprint

    return app

Bcrypt is now imported and initialized.

2 - Updating our model

In app/models/user.py we can now add some methods to use bcrypt.

# models/user.py
# http://docs.sqlalchemy.org/en/latest/orm/extensions/declarative/basic_use.html

from .base import Base
from ..bcrypt import bc
from ..database import db

class User(Base):

    __tablename__ = 'users'

    username = db.Column(db.String, nullable=False, unique=True)
    email = db.Column(db.String, nullable=False, unique=True)
    encrypted_password = db.Column(db.String, nullable=False)

    def set_password(self, password):
        self.encrypted_password = bc.generate_password_hash(password)

    def verify_password(self, password):
        return bc.check_password_hash(self.encrypted_password, password)

4 - Creating our routes

In app/api_v1, let’s create a file user.py for the routes of the user :

# assuming you're in flask_learning/my_app_v4 (venv)
touch app/api_v1/user.py

We import those routes in our module app/api_v1/__init__.py.

# app/api_v1/__init__.py

from flask import Blueprint

root_blueprint = Blueprint('api_v1', __name__)
api_v1_blueprint = Blueprint('api_v1', __name__, url_prefix='/api/v1')

# Import any endpoints here to make them available
from . import hello
from . import user

4.1 - Signup route

To signup, the route will receive a username, an email and a password.

In app/api_v1/user.py

# app/api_v1/user.py

from flask import (
    jsonify, request
from . import api_v1_blueprint
from ..database import db
from ..models.user import User

@api_v1_blueprint.route('/signup', methods=['POST'])
def signup():
    datas = request.get_json()
    username = datas.get('username','')
    if username is '':
        return jsonify(error="username is empty"),422
    email = datas.get('email','')
    if email is '':
        return jsonify(error="email is empty"),422
    # we could verify that this email is valid
    password = datas.get('password','')
    if password is '':
        return jsonify(error="password is empty"),422
    if User.query.filter(User.username == username).first() is not None:
        return jsonify(err="username already taken"), 409
    if User.query.filter(User.email == email).first() is not None:
        return jsonify(err="email already signed-up"), 409
    new_user = User()
    new_user.username = username
    new_user.email = email
    return jsonify(msg="welcome :-)"), 200

Explaining : - line 15 : reading the json we received - lines 17 to 26 : checking that the differents JSON fields are correct (not empty etc…) - lines 27-28 : calling the controller to create the user - line 29 : if the controller does not raise any exception, we can proceed - lines 30-31 : return the error

4.1.1 - Adding the unit test

In our folder tests, let’s add a file test_2_signup_route.py : (we add a number to order the tests)

# tests/test_2_signup_route.py

def test_signup_empty_password(client):
    # testing errors
    empty_password = client.post("/api/v1/signup", json={
        'username': 'testuser', 'password': '', 'email': 'test_user@mail.com'
    assert empty_password.status_code == 422

def test_signup_empty_username(client):
    empty_username = client.post("/api/v1/signup", json={
        'username': '', 'password': 'test_user', 'email': 'test_user@mail.com'
    assert empty_username.status_code == 422

def test_signup_empty_email(client):
    empty_email = client.post("/api/v1/signup", json={
        'username': 'testuser', 'password': 'test_user', 'email': ''
    assert empty_email.status_code == 422

def test_signup_correct(client):
    correct = client.post("/api/v1/signup", json={
        'username': 'testuser', 'password': 'test_user', 'email': 'test_user@mail.com'
    assert correct.status_code == 200

def test_signup_username_taken(client):
    username_taken = client.post("/api/v1/signup", json={
        'username': 'testuser', 'password': 'test_user', 'email': 'test_user@mail.com'
    assert username_taken.status_code == 409

def test_signup_email_taken(client):
    email_taken = client.post("/api/v1/signup", json={
        'username': 'testuser', 'password': 'test_user', 'email': 'test_user@mail.com'
    assert email_taken.status_code == 409

v4 unittest

4.1.2 - Testing this signup route

Let’s run our app, initiate the database and test this route :-)

# assuming you're in flask_learning/my_app_v4 (venv)
flask reset-db
flask run

Perfect, our app is working great :)

A quick check inside the database to be sure the data is stored :

v4 sqlitebrowser check

The password is encrypted and our user is there, no problem !

4.2 - Login

In app/api_v1/user.py, at the end of the file, let’s add our login route :

# app/api_v1/user.py


@api_v1_blueprint.route('/login', methods=['POST'])
def login():
    datas = request.get_json()
    username = datas.get('username','')
    if username is '':
        return jsonify(error="username is empty"),422
    password = datas.get('password','')
    if password is '':
        return jsonify(error="password is empty"),422
    user = User.query.filter(User.username == username).first()
    if user is not None:
        if user.verify_password(password):
            return jsonify(msg="welcome"), 200
        return jsonify(err="password incorrect"), 401
    return jsonify(err="username incorrect"), 404

4.2.1 - Adding the unit test

In our folder tests, let’s add a file test_3_login_route.py : (we add a number to order the tests)

# tests/test_3_login_route.py

def test_empty_password(client):
    # testing errors
    empty_password = client.post("/api/v1/login", json={
        'username': 'testuser', 'password': ''
    assert empty_password.status_code == 422

def test_empty_username(client):
    empty_username = client.post("/api/v1/login", json={
        'username': '', 'password': 'test_user'
    assert empty_username.status_code == 422

def test_correct(client):
    correct = client.post("/api/v1/login", json={
        'username': 'testuser', 'password': 'test_user'
    assert correct.status_code == 200

def test_wrong_username(client):
    wrong_username = client.post("/api/v1/login", json={
        'username': 'testusernot', 'password': 'test_user'
    assert wrong_username.status_code == 404

def test_wrong_password(client):
    wrong_password = client.post("/api/v1/login", json={
        'username': 'testuser', 'password': 'test_user_wrong'
    assert wrong_password.status_code == 401

v4 unittest

4.2.1 - Testing this login route

Let’s run our app :

# assuming you're in flask_learning/my_app_v4 (venv )
flask run 

Success :

v4 postman login example

Fail :

v4 postman login error

Success :

v4 httpie login example

Fail :

v4 httpie login error


If you’re stuck or don’t understand something, feel free to drop me an email / dm on twitter / a comment below. You can also take a look at flask_learning/flask_cybermooc/version_4 to see the reference code. And use run.sh to launch it.

Otherwise, congratulations ! You just learned how to create two main routes “login” and “signup”. (well your users aren’t technically logged-in but still)

If you understood everything, in part 5 you will see how to use JSON Web Tokens, a cool way to authentify your users.