# TurboGears 2 Configuration

TurboGears 2 provides a configuration system that attempts to be both extremely flexible for power users and very simple to use for standard projects.

## Overview

The application configuration is separated from the deployment specific information. In TurboGears 2.3.6 there is a config module, containing several configuration specific python files – these are done in python (not as INI files), because they actually setup the TurboGears 2.3.6 application and its associated WSGI middleware. Python provides an incredibly flexible config system with all kinds of tools to keep you from having to repeat yourself. But it comes with some significant drawbacks, python is more complex than INI, and is less declarative so can be less obvious.

But we believe these drawbacks are more than overcome by the power and flexibility of python based configuration for the app because these files are intended to be edited only by application developers, not by those deploying the application. We’ve also worked hard to create an environment that is generally declarative.

At the same time the deployment level configuration is done in simple .ini files, in order to make it totally declarative, and easy for deployers who may not be python programmers.

## Configuration in the INI files

A TurboGears quickstarted project will contain a couple of .ini files which are used to define what WSGI app ought to be run, and to store end-user created configuration values, which is just another way of saying that the .ini files should contain deployment specific options.

By default TurboGears provides a `development.ini`, `test.ini`, and `production.ini` files. These are standard ini file formats.

These files are standard INI files, as used by PasteDeploy. The individual sections are marked off with `[]`‘s.

See also

Configuration file format and options are described in great detail in the Paste Deploy documentation.

If want to add some configuration option (let’s say an administrator’s email) here is how you would do so. First you would edit your `development.ini` file and go to the end of the `[app:main]` section.

You can then choose a sensible name for your configuration key and add it to the section:

    mail.from.administrator = someemail@somedomain.com

This would make sure this variable is now part of the configuration and can be accessed from anywhere in your code. For example let’s imagine that you wanted to get this config option from a controller’s code:

    import tg
    admin_emailfrom = tg.config.get('mail.from.administrator', 'notconfigured@nodomain.com')

If the person who deployed your application forgot to add the variable to his config file he would get the default value provided as the second argument of the get() call.

Warning

If you set a value like enable_subsystem = false, it will be loaded into python as the string ‘false’ which if used in a conditional will give you a very wrong result

The correct way of loading boolean values for your use is

    from paste.deploy.converters import asbool
    if asbool(config['enable_subsystem']):
       ... sub systems is enabled...

## Configuration Milestones

Since TurboGears 2.3 the configuration process got divided in various milestones, each of those milestones is bound to an advancement in the framework setup process.

Whenever a milestone is reached all the registered callbacks are fired and the configuration process can continue. If the milestone is already passed when a callback is registered, the callback gets instantly fired.

Note

The `tg.config` object is available at import time but until the configuration file is parsed, it only contains the system defaults. If you need to perform startup time setup based on the supplied configuration, you should do so in a milestone.

Milestones are available through the `tg.configuration.milestones` module, the currently provided milestones are:

- `milestones.config_ready` - Configuration file has been loaded and is

    available in `tg.config`

- `milestones.renderers_ready` - Renderers have been registered and all

    of them are available

- `milestones.environment_loaded` - Full environment have been loaded

    but application has not been created yet.

Registering an action to be executed whenever a milestone is reach can be done using `tg.configuration.milestones._ConfigMilestoneTracker.register()` method of each milestone. The registered action takes no parameters.

Milestones are much like Hooks but they are only related to the configuration process. The major difference is that while an hook can fire multiple times a milestone can be reached only once.

### Milestones and Hooks order of execution

The order of execution of the milestones and hooks provided during the application startup process is:

- `milestones.config_ready`
- startup Hook
- `milestones.renderers_ready`
- `milestones.environment_loaded`
- before_config Hook
- after_config Hook

## The config module

Tip

A good indicator of whether an option should be set in the `config` directory code vs. the configuration file is whether or not the option is necessary for the functioning of the application. If the application won’t function without the setting, it belongs in the appropriate config/ directory file. If the option should be changed depending on deployment, it belongs in the ini files.

Our hope is that 90% of applications don’t need to edit any of the config module files, but for those who do, the most common file to change is `app_config.py`:

    from tg.configuration import AppConfig
    import wiki20
    from wiki20 import model
    from wiki20.lib import app_globals, helpers

    base_config = AppConfig()
    base_config.renderers = []

    base_config.package = wiki20

    #Set the default renderer
    base_config.default_renderer = 'genshi'
    base_config.renderers.append('genshi')

    #Configure the base SQLALchemy Setup
    base_config.use_sqlalchemy = True
    base_config.model = wiki20.model
    base_config.DBSession = wiki20.model.DBSession

`app_cfg.py` exists primarily so that `middleware.py` and `environment.py` can import and use the `base_config` object.

The `base_config` object is an `AppConfig()` instance which allows you to access its attributes like a normal object, or like a standard python dictionary.

One of the reasons for this is that `AppConfig()` provides some defaults in its `__init__`. But equally important it provides us with several methods that work on the config values to produce the two functions that set up your TurboGears app.

We’ve taken care to make sure that the entire setup of the TurboGears 2.3.6 framework is done in code which you as the application developer control. You can easily customize it to your needs. If the standard config options we provide don’t do what you need, you can subclass and override `AppConfig` to get exactly the setup you want.

The `base_config` object that is created in `app_cfg.py` should be used to set whatever configuration values that belong to the application itself and are required for all instances of this app, as distinct from the configuration values that you set in the `development.ini` or `production.ini` files that are intended to be editable by those who deploy the app.

As part of the app loading process the `base_config` object will be merged in with the config values from the .ini file you’re using to launch your app, and placed in `tg.config`.

As we mentioned previously, in addition to the attributes on the `base_config` object there are a number of methods which are used to setup the environment for your application, and to create the actual TurboGears WSGI application, and all the middleware you need.

You can override `base_config`‘s methods to further customize your application’s WSGI stack, for various advanced use cases, like adding custom middleware at arbitrary points in the WSGI pipeline, or doing some unanticipated (by us) application environment manipulation.

And we’ll look at the details of how that all works in the advanced configuration section of this document.

## Configuring your application

Here’s are some of the more general purpose configuration attributes:

### Configuration Attributes

The configuration object has a number of attributes that automate the majority of what you need to do with the config object. These shortcuts eliminate the need to provide your own setup methods for configuring your TurboGears application.

#### Mimetypes

By default, only json/application and text/html are defined mimetypes. If you would like to use additional mime-types you must register them with your application’s config. You can accomplish this by adding the following code your your app_cfg.py file:

    base_config.mimetype_lookup = {'.ext':'my-mimetype'}

#### Static Files

`base_config.serve_static` – automatically set to `True` for you. Set to False if you have set up apache, or nginx (or some other server) to handles static files.

#### Request Extensions

`base_config.disable_request_extensions` – by default this is false. This means that TG will take the request, and strip anything off the end of the last element in the URL that follows ”.”. It will then take this information, and assign an appropriate mime-type and store the data in the tg.request.response_type and tg.request.response_ext variables. By enabling this flag, you disable this behavior, rendering TG unable to determine the mime-type that the user is requesting automatically.

#### Stand Alone

`base_config.stand_alone` – set this to `False` if you don’t want error handling, HTTP status code error pages, etc. This is intended for the case where you’re embedding the TG app in some other WSGI app which handles these things for you.

#### Cookie Secret

The `beaker.session.secret` key of the `base_config` object contains the secret used to store user sessions. TurboGears automatically generates a random secret for you when you create a project. If an attacker gets his hands on this key, he will be able to forge a valid session an use your application at though he was logged in. In the event of a security breach, you can change this key to invalidate all user sessions.

#### Authentication Character Set

Set `base_config.sa_auth.charset` to define the character encoding for your user’s login. This is especially important if you expect your users to have non-ascii usernames and passwords. To set it to utf-8, your add this to your app_config.py file.:

    base_config.sa_auth.charset = 'utf-8'

## Advanced Configuration

Sometimes you need to go beyond the basics of setting configuration options. We’ve created a number of methods that you can use to override the way that particular pieces of the TurboGears 2.3.6 stack are configured. The basic way you override the configuration within app.cfg looks something like this:

    from tg.configuration import AppConfig
    from tw2.core.middleware import TwMiddleware

    class MyAppConfig(AppConfig):

        def add_tosca2_middleware(self, app):

            app = TwMiddleware(app,
                default_engine=self.default_renderer,
                translator=ugettext,
                auto_reload_templates = False
                )

            return app
    base_config = MyAppConfig()

    # modify base_config parameters below

The above example shows how one would go about overridding the ToscaWidgets2 middleware. See the `AppConfig` for more ideas on how you could modify your own custom config