twcarbone / microblog Goto Github PK

Flask is a python framework that is used to build web applications. It uses the Jinja2 templating engine to render dynamic html content. This project follows the tutorial from this blog.

(a) Flask basic overview
(b) app.run() vs flask run

The basic structure of the project is outlined below.

microblog/
├── .flaskenv
├── .venv/
├── microblog.py
├── config.py
├── tests.py
├── requirements.txt
├── app/
│   ├── __init__.py
│   ├── routes.py
│   ├── forms.py
│   ├── errors.py
│   └── models.py
├── templates/
│   ├── index.html
│   └── 404.html
└── logs/

The recommended way to start the application is using the flask run command. The command starts a development server, loads environment variables from the .flaskenv file, and runs the python file defined by the FLASK_APP environment variable in .flaskenv. See reference (a) for further reading on flask run.

# .flaskenv
export FLASK_APP=microblog.py          # Name of application file
export FLASK=[development|production]  # Toggle development or production mode (among others)

If running on a remote server, use flask run -h 0.0.0.0 -p xxxx.

In this case, microblog.py imports the app module, calling app/__init__.py. This file will create the application object; import configuration data from config.py; initialize database and migrations objects; initialize the login manager; setup the mail server and application logging; and import routes.py, models.py, and errors.py.

Application configuration data is stored in config.py. For some configuration information, the file will first look check if any environment variables are set matching the configuration item. If not, config.py sets it. Other configuration information is located here for convenience.

All of the different URLs for the application are handled in routes.py. Each page is handled by a view function, which is mapped to a URL for the pages contained in app/templates/. When the client's browser requests a page, flask runs the corresponding view function for the page, passing any dynamic content to the template. The template is displayed using the Jinja2 templating engine. Each template is primarily standard html, with the expected dynamic content from routes.py encapsulated in double curly braces. Control statements, such as for loops or inclusion statements (e.g., import, #include) are denoted by {% %} markers.

A web page often accepts input from a user in some format. Where input is required, forms are implemented. Forms rely on the WTForms package and its associated lightweight flask warapper, Flask_WTF.

• The Form is the key building block of any web form
• Each Form contains several Fields, such as IntegerField or StringField
• Every Field has a Widget, which represents the actual rendered object
• Fields contain a list of Validators, such as DataRequired()

Simply put, there are a huge number of python packages that are required to build a flask application. Each package, its dependencies, and a brief description of the purpose of the package is provided here.