So, you want to develop an application with Python and weppy, huh? We should start with an example.

We will create a simple microblog application, using weppy and a database. SQLite comes out of the box with Python, so you won't need to download anything other than weppy.

If you want the full source code in advance, check out the example source.

Bloggy: a micro blog

We will call our blogging application bloggy and, basically, we want it to do the following things:

  • let users sign up and then sign in and out with their own credentials
  • let only an admin user add new posts (consisting of a title and a text body)
  • show all posts' titles in reverse order (newest on top) to everyone on the index page
  • show the entire post on a specific page and allow registered users to comment

– hem, dude.. seems like quite a lot of stuff for a "micro" blogging application
relax! you'll see that every feature will be short work with weppy

Application structure

Let's start from the basis, and create this directory structure:


The bloggy folder won't be a python package. It's just somewhere to drop our files. In the next steps, we will build our application with a single python file, since it's small. The files inside the static folder will be available to clients via HTTP. This is the place where you should put the CSS and JavaScript files. The templates you're gonna create later in this tutorial will go in the templates directory instead.

After you create the above folders, create a bloggy.py file inside your bloggy application:

from weppy import App

app = App(__name__)

so you should end with this directory structure:


Now you can test your application simply issuing the following command (inside the bloggy folder):

> weppy --app bloggy.py run

and you will see a message telling you that the server has started, along with the address at which you can access it.

When you head over to the server in your browser, you will get a 404 Page Not Found error because we don’t have any exposed function yet. However, we will attend to that a little later on. First, we should create the database for the application.

Database schema

The first step in coding our application is to create the database schema. In bloggy, we need at least 4 tables:

  • The users table
  • A users' groups/permission table (to allow only the admin user to write posts)
  • The posts table
  • The comments table

Now, this might sounds complicated, but it's actually not. In fact, we can skip all the schema about users since weppy includes an authorization module that creates the tables we need automatically.

So, how will we build our schema? We will use the default AuthUser class for the users table and authorization system, and the Model class for the other tables:

from weppy import request, session
from weppy.dal import Field, Model, belongs_to, has_many
from weppy.tools.auth import AuthUser

class User(AuthUser):
    # will create "users" table and groups/permissions ones
    has_many('posts', 'comments')

class Post(Model):

    title = Field()
    text = Field('text')
    date = Field('datetime')

    default_values = {
        'user': lambda: session.auth.user.id,
        'date': lambda: request.now
    validation = {
        'title': {'presence': True},
        'text': {'presence': True}
    form_rw = {
        'user': False,
        'date': False

class Comment(Model):
    belongs_to('user', 'post')

    text = Field('text')
    date = Field('datetime')

    default_values = {
        'user': lambda: session.auth.user.id,
        'date': lambda: request.now
    validation = {
        'text': {'presence': True}
    form_rw = {
        'user': False,
        'post': False,
        'date': False

That's it. You can see we defined some relations between our models, which will be a relationships between the tables, so we have these conditions:

  • a post always have one author, and an author can have many posts
  • a comment always have one author and always refers to one post, and a post can have many comments

Moreover, we have set some default values (like the dates and the authors) and we have hidden some fields in forms to the users: it would be pointless to have an user field if the user could set this value to whatever he or she wanted. Accordingly, we're telling to weppy to auto-set those values to the right ones.

We've also added some validation, so we can prevent users from sending empty posts or comments.

Initialize the database and the auth module

We've defined our schema, so now it's time to add the database and the authorization system to bloggy. It's as simple as writing:

from weppy import DAL
from weppy.tools import Auth

db = DAL(app)
auth = Auth(app, db, usermodel=User)
db.define_models(Post, Comment)

But, wait, how do we add an admin user who can write posts? We can write a setup function which allows us to do that. Let's write:

def setup():
    # create the user
    user = User.create(
    # create an admin group
    admins = auth.add_group("admin")
    # add user to admins group
    auth.add_membership(admins, user.id)

The code is quite self-explanatory: it will add an user who can sign in with the "walter@massivedynamics.com" email and "pocketuniverse" as their password, then it creates an admin group and adds the Walter user to this group.

Also, notice that we added the @app.command decorator, which allow us to run our setup function using the weppy command shell:

> weppy --app bloggy.py setup

Now that the backend is ready, we can prepare to write and expose our functions.

Exposing functions

Before we can start writing the functions that will handle the clients' requests, we need to add the database and authorization handlers to our application, so that we can use them with our functions following the request flow.

Moreover, to use the authorization module, we need to add a sessions manager to the application's handlers, too. In this tutorial, cookie support for session will be enough, and we will use "Walternate" as a secret key for encrypting cookies.

from weppy.sessions import SessionCookieManager
app.common_handlers = [

Then, we can start writing the function for our index page, which will list all the posts in reverse chronological order.

def index():
    posts = Post.all().select(orderby=~Post.date)
    return dict(posts=posts)

Since this list will only show up the posts' titles, we also write a function to retrieve details for a single post:

from weppy import abort

def one(pid):
    def _validate_comment(form):
        # manually set post id in comment form
        form.params.post = pid
    # get post and return 404 if doesn't exist
    post = Post.get(pid)
    if not post:
    # get comments and create a form
    comments = post.comments(orderby=~Comment.date)
    form = Comment.form(onvalidation=_validate_comment)
    if form.accepted:
        redirect(url('one', pid))
    return locals()

As you can see, the one function will show the post text, the comments users have written about it, and a form that allows users to add new comments.

We also need to expose a function to write posts, and it will be available only to users in the "admin" group, thanks to the requires decorator:

from weppy import redirect, url
from weppy.tools import requires

@requires(lambda: auth.has_membership('admin'), url('index'))
def new_post():
    form = Post.form()
    if form.accepted:
        redirect(url('one', form.params.id))
    return dict(form=form)

If a user tries to open the "/new" address without being a member of the admin group, weppy will redirect them to the index page.

Finally, we should expose an account function to let users sign up and sign in on bloggy:

def account(f, k):
    form = auth(f, k)
    return dict(form=form)

Now that we have all the main code of our application ready to work, we need the templates to render the content to the clients.

The templates

We should create a template for every function we exposed. However, since the weppy templating system supports blocks and nesting, and we don't really want to repeat ourselves when writing code, we will start with a main layout file under templates/layout.html, and we will extend it with the functions' templates:

<!DOCTYPE html>
        {{include_static 'style.css'}}
        <div class="page">
            <a href="/" class="title"><h1>Bloggy</h1></a>
            <div class="nav">
            {{if not current.session.auth:}}
                <a href="{{=url('account', 'login')}}">log in</a>
                <a href="{{=url('account', 'logout')}}">log out</a>
            {{block main}}

All the templates we will create from now, will start with an extend instruction. Their contents will be injected on the include instruction of the main layout.

Starting with index.html (which will be used with our index function):

{{extend 'layout.html'}}

<a href="{{=url('new_post')}}">Create a new post</a>
<ul class="posts">
{{for post in posts:}}
        <a href="{{=url('one', post.id)}}">Read more</a>
        <hr />
{{if not posts:}}
    <li><em>No posts here so far.</em></li>

Then, the one.html template which, is the most complex:

{{extend 'layout.html'}}

<br />
<hr />
{{if current.session.auth:}}
<h5>Write a comment:</h5>
<ul class="comments">
{{for comment in comments:}}
        <br />
        <em>by {{=comment.user.first_name}} on {{=comment.date}}</em>
{{if not comments:}}
    <li><em>No comments here so far.</em></li>

The two remaining templates are simpler and similar, since they will only show one form each. So, the first, new_post.html, will be just:

{{extend 'layout.html'}}

<h1>Create a new post</h1>

and account.html will be:

{{extend 'layout.html'}}


Some styling

Now that everything works, it's time to add some style to bloggy. We just create a style.css file inside static folder and write down something like this:

body           { font-family: sans-serif; background: #eee; }
a, h1, h2      { color: #377ba8; }
h1, h2, h4, h5 { font-family: 'Georgia', serif; }
h1             { border-bottom: 2px solid #eee; }
h2             { font-size: 1.2em; }

.page          { margin: 2em auto; width: 35em; border: 5px solid #ccc;
                 padding: 0.8em; background: white; }
.title         { text-decoration: none; }
.posts         { list-style: none; margin: 0; padding: 0; }
.posts li      { margin: 0.8em 1.2em; }
.posts li h2   { margin-left: -1em; }
.posts li hr   { margin-left: -0.8em; }
.nav           { text-align: right; font-size: 0.8em; padding: 0.3em;
                 margin-bottom: 1em; background: #fafafa; }

Go ahead

You've completed the tutorial, with a new blogging application written in very few lines, and simple ones at that. You should be more confident with the weppy workflow and its syntax, so feel free to start writing your own applications!

To explore all the features of weppy, and better understand what you've done in this tutorial, you should read the complete documentation, and try to expand this simple application with more features, so that it can better meet your needs.