Creating the Application

Now that we’re set up to create a Ligare application, let’s find out how to actually create one.

We will follow a structure that lets us write the application as a single Python “module,” similar to how python-guide.org demonstrates.

First create the module.

user@: my-ligare-app $ mkdir app
user@: my-ligare-app $ touch app/__init__.py

Now we need to add some code to __init__.py.

Let’s also explore a bit about how Ligare.web works.

First, Ligare.web uses a builder to set up an instance of your application during runtime. This allows us to build our application using specific functions to configure desired beavhiors and features.

See also

A builder is a pattern that helps programmers configure an instance of some other type. For this guide, it helps us configure an instance of FlaskApp, which is the class name for the type of application we’re creating.

The class we need for this is ApplicationBuilder[T]. We also need the application type. For this example, we’re using FlaskApp.

See also

A “generic” class is a way to specify generic functionality for a range of more specific types. Here, we use the generic class ApplicationBuilder[T] to configure generic aspects of FlaskApp. Here, the “generic type” is named T and is how we reference the more specific type that it represents.

Note

ApplicationBuilder[T] supports one other type of class called Flask. Review this guide to see how to create a Flask application.

Modify app/__init__.py with the following.

Review example sources [web-api/app/__init__.py]

Now we have something we can run. Go ahead and run this code.

user@: my-ligare-app $ python app/__init__.py

Unfortunately, it seems we have another step to take because the application tells us it cannot find its configuration file. That makes sense, because we haven’t created it yet.

ConfigInvalidError: The configuration file specified, `app/config.toml`,
could not be found at `/my-ligare-app/app/config.toml` and was not loaded.
Is the file path correct?

Let’s create that file.

user@: my-ligare-app $ cat > app/config.toml <<EOF
[logging]
format = 'plaintext'

[flask]
app_name = 'app'
EOF

Note

Due to a bug with JSON logging, plaintext logging must be configured. This format also makes it easier to read the output of your application in the console when you are building and testing it.

Run the application again.

user@: my-ligare-app $ python app/__init__.py

Now you will see this.

* Serving Flask app 'app'
* Debug mode: off
WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
* Running on http://localhost:5000
Press CTRL+C to quit

Congrats! Your application is running. Now you can visit http://localhost:5000 to see your application in action!

But it doesn’t do anything except tell you that nothing can be found.

{
  "error_msg": "The requested URL was not found on the server. If you entered the URL manually please check your spelling and try again.",
  "status": "Not Found",
  "status_code": 404
}

This is because, while we do have a functional web application, we still haven’t added any API endpoints to it.