Templates¶

Syntax¶

A Django template is a text document or a Python string marked-up using the Django template language. Some constructs are recognized and interpreted by the template engine. The main ones are variables and tags.

A template is rendered with a context. Rendering replaces variables with their values, which are looked up in the context, and executes tags. Everything else is output as is.

The syntax of the Django template language involves four constructs.

My first name is {{ first_name }}. My last name is {{ last_name }}.

My first name is John. My last name is Doe.

{{ my_dict.key }}
{{ my_object.attribute }}
{{ my_list.0 }}

{% csrf_token %}

{% cycle 'odd' 'even' %}

{% if user.is_authenticated %}Hello, {{ user.username }}.{% endif %}

{{ django|title }}

The Web Framework For Perfectionists With Deadlines

{{ my_date|date:"Y-m-d" }}

{# this won't be rendered #}

Components¶

Configuration¶

Templates engines are configured with the TEMPLATES setting. It’s a list of configurations, one for each engine. The default value is empty. The settings.py generated by the startproject command defines a more useful value:

TEMPLATES = [
    {
        "BACKEND": "django.template.backends.django.DjangoTemplates",
        "DIRS": [],
        "APP_DIRS": True,
        "OPTIONS": {
            # ... some options here ...
        },
    },
]

BACKEND is a dotted Python path to a template engine class implementing Django’s template backend API. The built-in backends are django.template.backends.django.DjangoTemplates and django.template.backends.jinja2.Jinja2.

Since most engines load templates from files, the top-level configuration for each engine contains two common settings:

• DIRS defines a list of directories where the engine should look for template source files, in search order.

• APP_DIRS tells whether the engine should look for templates inside installed applications. Each backend defines a conventional name for the subdirectory inside applications where its templates should be stored.

While uncommon, it’s possible to configure several instances of the same backend with different options. In that case you should define a unique NAME for each engine.

OPTIONS contains backend-specific settings.

Usage¶

The django.template.loader module defines two functions to load templates.

get_template(template_name, using=None)[sorgente]¶

This function loads the template with the given name and returns a Template object.

The exact type of the return value depends on the backend that loaded the template. Each backend has its own Template class.

get_template() tries each template engine in order until one succeeds. If the template cannot be found, it raises TemplateDoesNotExist. If the template is found but contains invalid syntax, it raises TemplateSyntaxError.

How templates are searched and loaded depends on each engine’s backend and configuration.

If you want to restrict the search to a particular template engine, pass the engine’s NAME in the using argument.

select_template(template_name_list, using=None)[sorgente]¶

select_template() is just like get_template(), except it takes a list of template names. It tries each name in order and returns the first template that exists.

If loading a template fails, the following two exceptions, defined in django.template, may be raised:

exception TemplateDoesNotExist(msg, tried=None, backend=None, chain=None)[sorgente]¶

This exception is raised when a template cannot be found. It accepts the following optional arguments for populating the template postmortem on the debug page:

backend

The template backend instance from which the exception originated.

tried

A list of sources that were tried when finding the template. This is formatted as a list of tuples containing (origin, status), where origin is an origin-like object and status is a string with the reason the template wasn’t found.

chain

A list of intermediate TemplateDoesNotExist exceptions raised when trying to load a template. This is used by functions, such as get_template(), that try to load a given template from multiple engines.

exception TemplateSyntaxError(msg)[sorgente]¶

This exception is raised when a template was found but contains errors.

Template objects returned by get_template() and select_template() must provide a render() method with the following signature:

Template.render(context=None, request=None)¶

Renders this template with a given context.

If context is provided, it must be a dict. If it isn’t provided, the engine will render the template with an empty context.

If request is provided, it must be an HttpRequest. Then the engine must make it, as well as the CSRF token, available in the template. How this is achieved is up to each backend.

Here’s an example of the search algorithm. For this example the TEMPLATES setting is:

TEMPLATES = [
    {
        "BACKEND": "django.template.backends.django.DjangoTemplates",
        "DIRS": [
            "/home/html/example.com",
            "/home/html/default",
        ],
    },
    {
        "BACKEND": "django.template.backends.jinja2.Jinja2",
        "DIRS": [
            "/home/html/jinja2",
        ],
    },
]

If you call get_template('story_detail.html'), here are the files Django will look for, in order:

• /home/html/example.com/story_detail.html ('django' engine)

• /home/html/default/story_detail.html ('django' engine)

• /home/html/jinja2/story_detail.html ('jinja2' engine)

If you call select_template(['story_253_detail.html', 'story_detail.html']), here’s what Django will look for:

• /home/html/example.com/story_253_detail.html ('django' engine)

• /home/html/default/story_253_detail.html ('django' engine)

• /home/html/jinja2/story_253_detail.html ('jinja2' engine)

• /home/html/example.com/story_detail.html ('django' engine)

• /home/html/default/story_detail.html ('django' engine)

• /home/html/jinja2/story_detail.html ('jinja2' engine)

When Django finds a template that exists, it stops looking.

It’s possible – and preferable – to organize templates in subdirectories inside each directory containing templates. The convention is to make a subdirectory for each Django app, with subdirectories within those subdirectories as needed.

Do this for your own sanity. Storing all templates in the root level of a single directory gets messy.

To load a template that’s within a subdirectory, use a slash, like so:

get_template("news/story_detail.html")

Using the same TEMPLATES option as above, this will attempt to load the following templates:

• /home/html/example.com/news/story_detail.html ('django' engine)

• /home/html/default/news/story_detail.html ('django' engine)

• /home/html/jinja2/news/story_detail.html ('jinja2' engine)

In addition, to cut down on the repetitive nature of loading and rendering templates, Django provides a shortcut function which automates the process.

render_to_string(template_name, context=None, request=None, using=None)[sorgente]¶

render_to_string() loads a template like get_template() and calls its render() method immediately. It takes the following arguments.

template_name

The name of the template to load and render. If it’s a list of template names, Django uses select_template() instead of get_template() to find the template.

context

A dict to be used as the template’s context for rendering.

request

An optional HttpRequest that will be available during the template’s rendering process.

using

An optional template engine NAME. The search for the template will be restricted to that engine.

Usage example:

from django.template.loader import render_to_string

rendered = render_to_string("my_template.html", {"foo": "bar"})

See also the render() shortcut which calls render_to_string() and feeds the result into an HttpResponse suitable for returning from a view.

Finally, you can use configured engines directly:

engines¶

Template engines are available in django.template.engines:

from django.template import engines

django_engine = engines["django"]
template = django_engine.from_string("Hello {{ name }}!")

The lookup key — 'django' in this example — is the engine’s NAME.

Built-in backends¶

class DjangoTemplates[sorgente]¶

Set BACKEND to 'django.template.backends.django.DjangoTemplates' to configure a Django template engine.

When APP_DIRS is True, DjangoTemplates engines look for templates in the templates subdirectory of installed applications. This generic name was kept for backwards-compatibility.

DjangoTemplates engines accept the following OPTIONS:

• 'autoescape': a boolean that controls whether HTML autoescaping is enabled.

  It defaults to True.

  Avvertimento

  Only set it to False if you’re rendering non-HTML templates!

• 'context_processors': a list of dotted Python paths to callables that are used to populate the context when a template is rendered with a request. These callables take a request object as their argument and return a dict of items to be merged into the context.

  It defaults to an empty list.

  See RequestContext for more information.

• 'debug': a boolean that turns on/off template debug mode. If it is True, the fancy error page will display a detailed report for any exception raised during template rendering. This report contains the relevant snippet of the template with the appropriate line highlighted.

  It defaults to the value of the DEBUG setting.

• 'loaders': a list of dotted Python paths to template loader classes. Each Loader class knows how to import templates from a particular source. Optionally, a tuple can be used instead of a string. The first item in the tuple should be the Loader class name, and subsequent items are passed to the Loader during initialization.

  The default depends on the values of DIRS and APP_DIRS.

  See Loader types for details.

• 'string_if_invalid': the output, as a string, that the template system should use for invalid (e.g. misspelled) variables.

  It defaults to an empty string.

  See How invalid variables are handled for details.

• 'file_charset': the charset used to read template files on disk.

  It defaults to 'utf-8'.

• 'libraries': A dictionary of labels and dotted Python paths of template tag modules to register with the template engine. This can be used to add new libraries or provide alternate labels for existing ones. For example:

  OPTIONS = {
      "libraries": {
          "myapp_tags": "path.to.myapp.tags",
          "admin.urls": "django.contrib.admin.templatetags.admin_urls",
      },
  }
  

  Libraries can be loaded by passing the corresponding dictionary key to the {% load %} tag.

• 'builtins': A list of dotted Python paths of template tag modules to add to built-ins. For example:

  OPTIONS = {
      "builtins": ["myapp.builtins"],
  }
  

  Tags and filters from built-in libraries can be used without first calling the {% load %} tag.

class Jinja2[sorgente]¶

Requires Jinja2 to be installed:

$ python -m pip install Jinja2

...\> py -m pip install Jinja2

Set BACKEND to 'django.template.backends.jinja2.Jinja2' to configure a Jinja2 engine.

When APP_DIRS is True, Jinja2 engines look for templates in the jinja2 subdirectory of installed applications.

The most important entry in OPTIONS is 'environment'. It’s a dotted Python path to a callable returning a Jinja2 environment. It defaults to 'jinja2.Environment'. Django invokes that callable and passes other options as keyword arguments. Furthermore, Django adds defaults that differ from Jinja2’s for a few options:

• 'autoescape': True

• 'loader': a loader configured for DIRS and APP_DIRS

• 'auto_reload': settings.DEBUG

• 'undefined': DebugUndefined if settings.DEBUG else Undefined

Jinja2 engines also accept the following OPTIONS:

• 'context_processors': a list of dotted Python paths to callables that are used to populate the context when a template is rendered with a request. These callables take a request object as their argument and return a dict of items to be merged into the context.

  It defaults to an empty list.

  Using context processors with Jinja2 templates is discouraged.

  Context processors are useful with Django templates because Django templates don’t support calling functions with arguments. Since Jinja2 doesn’t have that limitation, it’s recommended to put the function that you would use as a context processor in the global variables available to the template using jinja2.Environment as described below. You can then call that function in the template:

  {{ function(request) }}
  

  Some Django templates context processors return a fixed value. For Jinja2 templates, this layer of indirection isn’t necessary since you can add constants directly in jinja2.Environment.

  The original use case for adding context processors for Jinja2 involved:

  • Making an expensive computation that depends on the request.

  • Needing the result in every template.

  • Using the result multiple times in each template.

  Unless all of these conditions are met, passing a function to the template is more in line with the design of Jinja2.

The default configuration is purposefully kept to a minimum. If a template is rendered with a request (e.g. when using render()), the Jinja2 backend adds the globals request, csrf_input, and csrf_token to the context. Apart from that, this backend doesn’t create a Django-flavored environment. It doesn’t know about Django filters and tags. In order to use Django-specific APIs, you must configure them into the environment.

For example, you can create myproject/jinja2.py with this content:

from django.templatetags.static import static
from django.urls import reverse

from jinja2 import Environment


def environment(**options):
    env = Environment(**options)
    env.globals.update(
        {
            "static": static,
            "url": reverse,
        }
    )
    return env

and set the 'environment' option to 'myproject.jinja2.environment'.

Then you could use the following constructs in Jinja2 templates:

<img src="{{ static('path/to/company-logo.png') }}" alt="Company Logo">

<a href="{{ url('admin:index') }}">Administration</a>

The concepts of tags and filters exist both in the Django template language and in Jinja2 but they’re used differently. Since Jinja2 supports passing arguments to callables in templates, many features that require a template tag or filter in Django templates can be achieved by calling a function in Jinja2 templates, as shown in the example above. Jinja2’s global namespace removes the need for template context processors. The Django template language doesn’t have an equivalent of Jinja2 tests.