Flask-Meld

Official Website - Flask-Meld.dev

Project inspiration - Ditch Javascript Frameworks For Pure Python Joy

Join the community on Discord - https://discord.gg/DMgSwwdahN

Meld is a framework for Flask to meld your frontend and backend code. What does that mean? It means you can enjoy writing dynamic user interfaces in pure Python.

Less context switching. No need to write javascript. More fun!

Initialize Meld in your project

For the sake of example, here is a minimal Flask application to get things running:

from flask import Flask, render_template
from flask_meld import Meld

app = Flask(name)
app.config['SECRET_KEY'] = 'big!secret'
meld = Meld()
meld.init_app(app)
socketio = app.socketio
@app.route('/')
def index():
    return render_template("base.html")
if name == 'main':
    socketio.run(app, debug=True)

Add

{% meld_scripts %}

to your base html template

This sets up the application and initializes Flask-Meld.

    <title>Meld Example</title>


    <div>
    <!-- Add the line below to include the necessary meld scripts-->
    {% meld_scripts %}

    {% block content %}
        <!-- Using a component in your template is easy! -->
        {% meld 'counter' %}
    {% endblock %}
    </div>
    <style>
    </style>

Components

Components are stored in

meld/components

Components are simple Python classes.

The

counter

# app/meld/components/counter.py

from flask_meld.component import Component
class Counter(Component):
    count = 0
def add(self):
    self.count = int(self.count) + 1

def subtract(self):
    self.count = int(self.count) - 1

Templates

Create a component template in

templates/meld/counter.html

templates/meld

{% meld 'counter' %}

Here is an example for counter:

    -
    
    +

Let's take a look at that template file in more detail.

The buttons use

meld:click

add

subtract

meld:model

count

Modifiers

Use modifiers to change how Meld handles network requests.

debounce

debounce-250

defer

search

prevent

defer

enter

meld:submit.prevent="search"

search

<!-- To get the same functionality without using meld:submit.prevent="search" you
would need to add an event listener for the enter key 
<input meld:model.defer="search_text" meld:keydown.Enter="search" type="text" name="name" id="name" placeholder="Search for name">
-->

Form Validation

A big part of creating web applications is using forms. Flask-Meld integrates with Flask-WTF to give you real-time form validation without writing any Javascript.

Use WTForms for validation

Define your form with Flask-WTF just as you always do.

# forms.py
from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField
from wtforms.validators import DataRequired, Email, EqualTo


class RegistrationForm(FlaskForm):
    email = StringField('Email', validators=[DataRequired(), Email()])
    password = PasswordField('Password', validators=[DataRequired()])
    password_confirm = PasswordField('Confirm Password', validators=[DataRequired(), EqualTo('password')])

Create your template

Use WTForm helpers to create your form in your HTML template.

    
        

            {{ form.email.label }}
            {{ form.email }}
             {{ errors.password | first }} 
        

    <div>
        {{ form.password.label }}
        {{ form.password }}
        <span> {{ errors.password | first }} </span>
    </div>
    <div>
        {{ form.password_confirm.label }}
        {{ form.password_confirm }}
        <span> {{ errors.password_confirm | first }} </span>
    </div>
    <div>
        {{ form.submit }}
    </div>
</form>

Using the WTForm helpers saves you some typing. Alternatively, you can define your HTML form without using the helpers. For example, to make a field use

meld:model="name_of_field"

Define the form in the component

# meld/components/register.py
from flask_meld import Component
from forms import RegistrationForm


class Register(Component):
    form = RegistrationForm()

Realtime form validation

To make your form validate as a user types use the

updated

validate

# meld/components/register.py
from flask_meld import Component
from forms import RegistrationForm


class Register(Component):
    form = RegistrationForm()
def updated(self, field):
    self.validate(field)

Your routes can stay the same when using real-time validation

You have options here, you can create a custom method on your component to handle submissions or you can use your regular old Flask routes.

@app.route('/register', methods=['GET', 'POST'])
def register():
    form = RegistrationForm()
    if form.validate_on_submit():
        # do anything you need with your form data...
        return redirect(url_for("index"))
    return render_template("register_page.html")

Pretty simple right? You can use this to create very dynamic user interfaces using pure Python and HTML. We would love to see what you have built using Meld so please share!