flask.md

Creating a New Flask App

Create the project's directory

mkdir MyNewFlaskApp cd MyNewFlaskApp

Install Flask

pip install Flask

Create & activate the project's virtual environment

python3 -m venv venv . venv/bin/activate

Create the directory & file that will hold the app's main Python code

mkdir flaskr touch __init__.py

• Adding an __init__.py file to a directory tells Python to treat it as a package rather than a module. Though it can be left empty, it usually contains code used to initialize a package. We can use it to house our main application code.

Basic layout in Python file (e.g. __init__.py)

import flask from Flask

def create_app( test_config=None ):
    app = Flask( __name__, instance_relative_config=True )
    ...
    return app

• See full tutorial here.

Set environment variables & run the application\

export FLASK_APP=flaskr
export FLASK_ENV=development
flask run

• Make these are run from the project's directory, not within the flaskr directory.

About Flask

• A Flask app is an instance of the Flask class. However, instead of using just one, global Flask object, a Flask app is best implemented by defining a function (e.g. create_app()) that creates and returns an instance of the Flask class whenever called. This function is often referred to as the "Application Factory." See the Flask tutorial for further details.

• Note that the create_app() function takes the name of a configuration file, which contains the names and values of environmental variables to be used by the Flask application.

About Virtual Environments

• Using a python virtual environment in a project is a way to ensure all of project's dependencies (e.g. python version, python packages, etc.) "accompany" it and are met wherever it happens to be run.

• Here's the Flask documentation on virtual environments.

• To add a virtual environment to a project, cd into the project's directory and run python3 -m venv venv

• Whenever you work on your project, activate its virtual environment first, by running . venv/bin/activate

About SQLite

• SQLite is a serverless relational database. Simply put, it allows you to implement a database in your project without having to run/connect to a separate database server.

• It's intended for light use, ideal for a development environment (or in production with light activity).

• Python also has built-in support for SQLite3, so there's no need to install it. Adding it to a project is a simple as import sqlite3. Further Flask-specific documentation is available here.

• A tutorial on using Flask with SQLAlchemy to interface with a SQLite database in a more object-oriented way can be found here.

Adding a UI

Bootstrap

• Bootstrap provides a large selection of pre-made UI components.

• To enable using Bootstrap via CDN: 1. Paste this into your HTML document's header, before any other links to css: <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">

  1. Paste these in order near the very of your HTML document, right bofore the </body> closing tag:

    <script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js" integrity="sha384-ZMP7rVo3mIykV+2+9J3UJ46jBk0WLaUAdn689aCwoqbBJiSnjAK/l8WvCWPIPm49" crossorigin="anonymous"></script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js" integrity="sha384-ChfqqxuZUCnJSK3+MXmPNIyE6ZbWh2IMqE241rYiqJxyMiZ6OW/JmZQ5stwEULTy" crossorigin="anonymous"></script>

• The full set-up instructions can also be found here.

• Most Bootstrap elements are added by creating a <div> with the class attribute set to one of Bootstrap's predefined classes. For example, adding a Boostrap alert element consists of the following: <div class="alert alert-primary" role="alert">A simple primary alert—check it out!</div>

  • Bootstrap uses the role attribute to ensure accessability.

Icons

• To enable use of free FontAwesome icons via CDN, add the following link tag to the header of your HTML document: <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.4.1/css/all.css" integrity="sha384-5sAR7xN1Nv6T6+dT2mhtzEpVJvfS3NScPQTrOxhwjIuvcA67KV2R5Jz6kr4abQsz" crossorigin="anonymous">

• To add a specific icon, pick the one you want from the FontAwesome gallery, then simply copy its html tag (e.g. <i class="fas fa-arrow-alt-circle-up"></i>) and paste it into the desired section of your HTML document.

Brad Nesbitt 10/26/2018