How to split a Flask application into parts

Introduction

An application is split into parts with blueprints.

You can read about them in more detail here .

This article is a step-by-step guide

Prerequisites

You have the main file __init__.py or app.py in which you have already created the Flask application

The urls are served with @app.route

Suppose you have a group of urls like

@app.route('/first/1', methods = ['GET']) … @app.route('/first/2', methods = ['GET']) … @app.route('/first/3', methods = ['GET']) …

and a group of urls like

@app.route('/second/1', methods = ['GET']) … @app.route('/second/2', methods = ['GET']) … @app.route('/second/3', methods = ['GET']) …

The urls that start with second you want to move into a separate sub-application, or you simply want to split the main file into parts so that the code is easier to find.

You have to do several things, the first of which is to create a new .py file

A new file

Next to the main file create a new file second.py

Import there everything you needed for it to work + functools

From flask be sure to import Blueprint it is the key module for this operation.

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

After the import add the line

bp = Blueprint('api', __name__, url_prefix='/second')

url_prefix='/second' means that all urls in this sub-application start with second

Add your urls, but replace @app. with @bp. and there is no need to write second/ any more

@bp.route('/1', methods = ['GET']) … @bp.route('/2', methods = ['GET']) … @bp.route('/3', methods = ['GET']) …

The file second.py is ready

Registering a new blueprint

Now in the main file, which is most likely called __init__.py, delete the moved urls

And register the new sub-application by declaring its blueprint

from . import second app.register_blueprint(second.bp)

url_for

You have most likely used url_for, and in the original file it looked something like this:

{{ url_for('second/1') }}

But now / has to be replaced with .

{{ url_for('second.1') }}

For the sake of order it also makes sense to move the templates into a separate folder templates/

open_resource

If you used to write with app.open_resource, now you have to write with bp.open_resource

For example:

def load_db(): with bp.open_resource('file.json') as f: return json.load(f)

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