Local settings for Django projects

This package attempts to solve the problem of handling local settings in Django projects. Local settings by definition can't be pre-defined, although perhaps they can have a reasonable default value (mainly useful for development). Another class of local settings are secret settings; these definitely shouldn't be pre-defined and should never be added to version control.

The problems with local settings are:

• How to specify which settings are local
• How to inform others which settings are local (or secret)
• How to actually give the local settings a value
• How to verify that local settings have been given a valid value
• How to ensure new local settings get set
• How to ensure local (and esp. secret) settings don't get added to version control

One common approach is to create a local settings template module with dummy/default values. When new developers start working on a project, they copy this file (e.g., local_settings.py.template => local_settings.py), which is typically excluded from version control. This approach at least identifies which settings are local, but it's not very convenient with regard to setting values and ensuring those values are valid. Also, instead of giving you a friendly heads-up when you forget to set a local setting, it barfs out an exception.

This package takes the approach that there will be only one settings module per project in the standard location: {project}.settings. That module defines/overrides Django's base settings in the usual way plus it defines which settings are local and which are secret.

In addition to the settings module, there will be one or more settings files. These are standard INI files with the added twist that the values are JSON encoded. The reasoning behind this is to use a simple, standard config file format while still allowing for easy handling of non-string settings.

TODO: Maybe add support for different config file format (e.g., YAML)?

Once the local settings are defined, any missing settings will be prompted for in the console (with pretty colors and readline support).

Features

• Missing local settings will be prompted for (only when running on a TTY/console)
• Local settings can be defined with validators
• Local settings can be defined with doc strings
• Local settings can be nested in settings lists and dicts
• Settings files can extend from each other
• Settings values can be injected into other settings values using a special syntax (AKA interpolation, similar to the standard library's configparser)
• Includes a script to easily generate local settings files for different environments
• Supports Python 2.7 - 3.6 (using six)
• Supports Django 1.7 - 1.11

Basic usage

• At the top of your project's settings module, import the load_and_check_settings function along with the types of settings you need:

    from local_settings import load_and_check_settings, LocalSetting, SecretSetting
  

• Then define some base settings and local settings:

    PACKAGE = 'top_level_package_name'
    DEBUG = LocalSetting(default=False)
    DATABASES = {
        'default': {
            'ENGINE': 'django.db.backends.postgresql',
            'NAME': LocalSetting(default='{{PACKAGE}}'),
            'USER': LocalSetting(''),
            'PASSWORD': SecretSetting(),
            'HOST': LocalSetting(''),
            'PORT': '',
        },
    }
    SECRET_KEY = SecretSetting(doc='The secret key for doing secret stuff')
  

  As you can see, local settings can be defined anywhere within the definition of a top level setting. They can also have doc strings, which are displayed when prompting.

  This also demonstrates interpolation. The DATABASES.default.NAME setting will be replaced with the PACKAGE setting, so that its default value is effectively 'top_level_package'.

• After all the local settings are defined, add the following lines:

    _settings = load_and_check_settings(globals())
    globals().update(_settings)
  

  These two lines merge the project's local settings into the settings module's namespace. Passing globals() initializes the local settings loader with base settings (e.g., PACKAGE in the example above) and by "telling" it which settings are local settings.

  load_and_check_settings() loads the project's local settings from a file ($PWD/local.cfg by default), prompting for any that are missing, and returns a new dictionary with local settings merged over any base settings. When not running on a TTY/console, missing local settings will cause an exception to be raised.

  globals().update(_settings) merges all of the settings into the settings module's namespace. After this line runs, you will be able to use the local settings just like any other settings. For example, you could do if DEBUG: ...; at this point, DEBUG is no longer a LocalSetting instance--it's a regular old bool.

  Note: You could just write globals().update(load_and_check_settings(globals())). The spelling above is just intended to make it more clear what's happening.

• Now you can run any manage.py command, and you will be prompted to enter any missing local settings. On the first run, the settings file will be created. On subsequent runs when new local settings are added to the settings module, the settings file will be appended to.

• Alternatively, you can run the included make-local-settings script to generate a local settings file.

Advanced usage

TODO: Discuss using multiple settings files, extending a settings file from another file, how to specify a settings file other than the default of local.cfg, editing settings files directly, &c.