Logan

Logan is a toolkit for running standalone Django applications. It provides you with tools to create a CLI runner, manage settings, and the ability to bootstrap the process.

Let's take the Sentry project for example, it specifies that it wants to use logan for running the application:

setup(
    name='sentry',
    install_requires=['logan'],
    entry_points={
        'console_scripts': [
            'sentry = logan.runner:run_app',
        ],
    },
)

It then defines several Django Management Commands as part of it's project, via the standard structure of sentry/management/commands/<command name>.py.

Now when we call sentry. it's actually piping that to the logan runner. Logan simply loads the predefined settings file (which defaults to PROJECT_CONF, or ~/.project/project.conf.py) and then passes the command off to Django's internal representation of django-admin.py. In this case, PROJECT is determined by the caller of logan.runner, which is "sentry". If it were "foo-bar", PROJECT would be FOO_BAR, and "project" would still be "foo-bar".

In most cases, you're also going to want to provide a default configuration to inherit from, as well as a template to generate for the user if their configuration does not exist.

To do this, within our sentry project we create a simple script, lets call put it in sentry/logan_runner.py:

from logan.runner import run_app

def generate_settings():
    """
    This command is run when ``default_path`` doesn't exist, or ``init`` is
    run and returns a string representing the default data to put into their
    settings file.
    """
    return ""

def main():
    run_app(
        project='sentry',
        default_config_path='~/.sentry/',
        default_settings='sentry.conf.defaults',
        settings_initializer='sentry.logan_runner.generate_settings',
        settings_envvar='SENTRY_CONF',
    )

if __name__ == '__main__':
    main()

We'd then slightly adjust our entry point in our setup.py:

setup(
    name='sentry',
    install_requires=['logan'],
    entry_points={
        'console_scripts': [
            'sentry = sentry.logan_runner:main',
        ],
    },
)

You'll now be able to access the sentry command as if it were django-admin.py. Even better, it will be configurable via an arbitrary settings file, and inherit any default settings you've specified:

# Note: run_gunicorn is provided by the gunicorn package
sentry run_gunicorn 0.0.0.0:8000 -w 3

Extra Applications

A need might come up to allow the user to register additional settings. These will automatically apply based on keynames prefixed with EXTRA_ assuming the base key (the latter part of the setting name) is of type list or tuple.

For example, to register additional INSTALLED_APPS, you would simply specify this in your custom (user) configuration:

EXTRA_INSTALLED_APPS = (
    'foo.bar',
)

This will ensure your default setting's INSTALLED_APPS do not have to be modified, and the user can specify additional apps with ease.

If you wish to disable this functionality, simply pass allow_extra=False to run_app:

run_app(
    # ...,
    allow_extras=False,
)