Flask application settings

Introduction

This section describes Flask's application-related settings.

View function

Here, as an example, the user authentication function is described as an example.

auth.py

import functools

from flask import (
    Blueprint, flash, g, redirect, render_template, request, session, url_for
)
from werkzeug.security import check_password_hash, generate_password_hash

from todo.db import get_db


bp = Blueprint('auth', __name__, url_prefix='/auth')


@bp.route('/signup', methods=('GET', 'POST'))
def signup():
    error = {}

    if request.method == 'POST':
        username = request.form['username']
        password = request.form['password']
        password_re = request.form['password-re']
        db = get_db()

        if not username:
            error['username'] = 'Please enter your user name.'

        if not password:
            error['password'] = 'Please enter your password.'

        if not password_re:
            error['password_re'] = 'Please enter the password (for confirmation).'
        
        if username and password and password_re:
            if password == password_re:
                registered_user = db.execute(
                    'SELECT id FROM user WHERE username=?', (username,)
                    ).fetchone()
                if registered_user is not None:
                    error['username'] = 'The user name is already registered.'
            else:
                error['password_re'] = 'The passwords do not match.'

        if error == {}:
            db.execute(
                'INSERT INTO user (username, password) VALUES (?, ?)',
                (username, generate_password_hash(password))
            )
            db.commit()
            return redirect(url_for('auth.login'))

    return render_template(
        'auth/form.html',
        type='signup',
        error=error
        )


@bp.route('/login', methods=('GET', 'POST'))
def login():
    error = None

    if request.method == 'POST':
        username = request.form['username']
        password = request.form['password']
        db = get_db()
        user = db.execute(
            'SELECT * FROM user WHERE username = ?', (username,)
        ).fetchone()

        if user is None or not check_password_hash(user['password'], password):
            error = 'The user name or password is incorrect.'

        if error is None:
            session.clear()
            session['user_id'] = user['id']
            return redirect(url_for('index'))

    return render_template(
        'auth/form.html',
        type='login',
        error=error
        )


@bp.before_app_request
def load_logged_in_user():
    user_id = session.get('user_id')

    if user_id is None:
        g.user = None
    else:
        g.user = get_db().execute(
            'SELECT * FROM user WHERE id = ?', (user_id,)
        ).fetchone()


@bp.route('/logout')
def logout():
    session.clear()
    return redirect(url_for('auth.login'))


def login_required(view):
    @functools.wraps(view)
    def wrapped_view(**kwargs):
        if g.user is None:
            return redirect(url_for('auth.login'))

        return view(**kwargs)

    return wrapped_view

Summary

This section describes the basics of setting up Flask applications. Next time, I'll cover HTML templates.