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Built-in context processors

By default, Django templates are enabled to have access to various variables. This eliminates the need to constantly declare widely used variables in every single Django view methods or as url extra options. These variables are made available through template context processors.

Django template context processors are explicitly defined in a project's settings.py file, in the TEMPLATES variable inside the OPTIONS key. By default and as illustrated in listing 3-1, Django projects are enabled with four context processors built-in to Django. Next, I'll describe the data variables made available by each of these context processors.

Django debug context processor (django.template.context_processors.debug)

The Django debug context processor exposes variables that are helpful for debugging. This context processor makes the following variables available on all Django templates:

Note The Django debug context processor displays variable values only if the requesting IP address is defined in the INTERNAL_IPS variable in settings.py. Even if the variables are declared in a template (e.g.{{debug}} or {{sql_queries}}) this restriction permits that only certain users view the debug messages in the template, while other users won't view anything.

For example, to view the debug and sql_queries values on your local workstation, add INTERNAL_IPS = ['127.0.0.1'] to the settings.py file. This tells Django to display these variables values for requests made from the IP address 127.0.0.1

Django request context processor (django.template.context_processors.request)

The Django request context processor exposes variables related to a request (i.e. HTTP request). This context processor makes data available through a massive dictionary named request, which includes some of the following key-values:

Django auth context processor (django.contrib.auth.context_processors.auth)

The Django auth context processor exposes variables related to authentication logic. This context processor makes the following variables accessible in Django templates:

Django messages context processor (django.contrib.messages.context_processors.messages)

The Django messages context processor exposes variables related to the Django messages framework, introduced in chapter 2. Messages are added in Django view methods to the message framework, which are then exposed in Django templates. This context processor makes the following variables accessible in Django templates:

Other built-in Django context processors: i18n, media, static, tz & CSRF context processors

The previous context processors offer some of the most common data required across all Django project templates, which is why they're enabled by default. However, this doesn't mean they are the only built-in Django context processors. There are in fact five more built-in context processors you can use to access certain data from all Django templates.

Django i18n context processor (django.template.context_processors.i18n)

The Django i18n context processor exposes variables related to internationalization logic. This context processor makes the following variables accessible in Django templates:

Django media context processor (django.template.context_processors.media)

The Django media context processor exposes a variable related to media resources. This context processor makes the following variable accessible in Django templates:

Django static context processor (django.template.context_processors.static)

The Django static context processor exposes a variable related to static resources. This context processor makes the following variable accessible in Django templates:

Tip Even though the static context processor is accesible (i.e. it's not deprecated) its functionality is outdated and should be avoided. You should use the staticfiles app instead. More details are provided in Chapter 5 in the section on setting up static web page resources (Images, CSS, JavaScript).

Django tz context processor (django.template.context_processors.tz)

The Django tz context processor exposes a variable related to a project's time zone. This context processor makes the following variable accessible in Django templates:

Django CSRF context processor (django.template.context_processors.csrf)

The Cross Site Request Forgeries (CSRF) context processor adds the csrf_token variable to all requests. This variable is used by the {% csrf_token %} template tag to protect against Cross Site Request Forgeries.

Although you can gain access to the csrf_token variable value in any Django template, you will have little -- if any -- need to expose it directly, as it's used as a security mechanism to detect forged requests. Chatper 7 covering the topic of Django forms describes what is and how CSRF works with Django.

Due to the security significance of having the csrf_token variable available on all requests, the CSRF context processor is always enabled -- irrespective of the context_processors list in OPTIONS -- and cannot be disabled.