Step 3: Installing flaskr as a Package

Flask is now shipped with built-in support for Click. Click provides Flask with enhanced and extensible command line utilities. Later in this tutorial you will see exactly how to extend the flask command line interface (CLI).

A useful pattern to manage a Flask application is to install your app following the Python Packaging Guide. Presently this involves creating two new files; setup.py and MANIFEST.in in the projects root directory. You also need to add an __init__.py file to make the flaskr/flaskr directory a package. After these changes, your code structure should be:

/flaskr
    /flaskr
        __init__.py
        /static
        /templates
        flaskr.py
        schema.sql
    setup.py
    MANIFEST.in

Create the setup.py file for flaskr with the following content:

from setuptools import setup

setup(
    name='flaskr',
    packages=['flaskr'],
    include_package_data=True,
    install_requires=[
        'flask',
    ],
)

When using setuptools, it is also necessary to specify any special files that should be included in your package (in the MANIFEST.in). In this case, the static and templates directories need to be included, as well as the schema.

Create the MANIFEST.in and add the following lines:

graft flaskr/templates
graft flaskr/static
include flaskr/schema.sql

Next, to simplify locating the application, create the file, flaskr/__init__.py containing only the following import statement:

from .flaskr import app

This import statement brings the application instance into the top-level of the application package. When it is time to run the application, the Flask development server needs the location of the app instance. This import statement simplifies the location process. Without the above import statement, the export statement a few steps below would need to be export FLASK_APP=flaskr.flaskr.

At this point you should be able to install the application. As usual, it is recommended to install your Flask application within a virtualenv. With that said, from the flaskr/ directory, go ahead and install the application with:

pip install --editable .

The above installation command assumes that it is run within the projects root directory, flaskr/. The editable flag allows editing source code without having to reinstall the Flask app each time you make changes. The flaskr app is now installed in your virtualenv (see output of pip freeze).

With that out of the way, you should be able to start up the application. Do this on Mac or Linux with the following commands in flaskr/:

export FLASK_APP=flaskr
export FLASK_DEBUG=true
flask run

(In case you are on Windows you need to use set instead of export). The FLASK_DEBUG flag enables or disables the interactive debugger. Never leave debug mode activated in a production system, because it will allow users to execute code on the server!

You will see a message telling you that server has started along with the address at which you can access it in a browser.

When you head over to the server in your browser, you will get a 404 error because we don’t have any views yet. That will be addressed a little later, but first, you should get the database working.

Externally Visible Server

Want your server to be publicly available? Check out the externally visible server section for more information.

Continue with Step 4: Database Connections.