Templates ========= A :term:`template` is a file on disk which can be used to render dynamic data provided by a :term:`view`. :mod:`repoze.bfg` offers a number of ways to perform templating tasks out of the box, and provides add-on templating support through a set of bindings packages. Out of the box, :mod:`repoze.bfg` provides templating via the :term:`Chameleon` templating library. :term:`Chameleon` provides support for two different types of templates: :term:`ZPT` templates and text templates. Before discussing how built-in templates are used in detail, we'll discuss two ways to render templates within :mod:`repoze.bfg` in general: directly, and via renderer configuration. .. index:: single: templates used directly single: Mako .. _templates_used_directly: Templates Used Directly ----------------------- The most straightforward way to use a template within :mod:`repoze.bfg` is to cause it to be rendered directly within a :term:`view callable`. You may use whatever API is supplied by a given templating engine to do so. :mod:`repoze.bfg` provides various APIs that allow you to render :term:`Chameleon` templates directly from within a view callable. For example, if there is a :term:`Chameleon` ZPT template named ``foo.pt`` in a directory in your application named ``templates``, you can render the template from within the body of a view callable like so: .. code-block:: python :linenos: from repoze.bfg.chameleon_zpt import render_template_to_response def sample_view(request): return render_template_to_response('templates/foo.pt', foo=1, bar=2) The ``sample_view`` :term:`view callable` above returns a :term:`response` object which contains the body of the ``template/foo.pt`` template. The template author will have the names ``foo`` and ``bar`` available as top-level names for replacement or comparison purposes. Every view must return a :term:`response` object (except for views which use a :term:`renderer`, which we'll see shortly). The :func:`repoze.bfg.chameleon_zpt.render_template_to_response` function is a shortcut function that actually returns a response object, but not all template APIs know about responses. When you use a template API that is "response-ignorant" you can also easily render a template to a string, and construct your own response object as necessary with the string as the body. For example, the :func:`repoze.bfg.chameleon_zpt.render_template` API returns a string. We can manufacture a :term:`response` object directly, and use that string as the body of the response: .. code-block:: python :linenos: from repoze.bfg.chameleon_zpt import render_template from webob import Response def sample_view(request): result = render_template('templates/foo.pt', foo=1, bar=2) response = Response(result) return response Because :term:`view callable` functions are typically the only code in :mod:`repoze.bfg` that need to know anything about templates, and because view functions are very simple Python, you can use whatever templating system you're most comfortable with within :mod:`repoze.bfg`. Install the templating system, import its API functions into your views module, use those APIs to generate a string, then return that string as the body of a :term:`WebOb` :term:`Response` object. For example, here's an example of using `Mako `_ from within a :mod:`repoze.bfg` :term:`view`: .. ignore-next-block .. code-block:: python :linenos: from mako.template import Template from webob import Response def make_view(request): template = Template(filename='/templates/template.mak') result = template.render(name=request.params['name']) response = Response(result) return response .. note:: If you use third-party templating languages without cooperating BFG bindings directly within view callables, the auto-template-reload strategy explained in :ref:`reload_templates_section` will not be available, nor will the template resource overriding capability explained in :ref:`overriding_resources_section` be available, nor will it be possible to use any template using that language as a :term:`renderer`. However, it's reasonably easy to write custom templating system binding packages for use under :mod:`repoze.bfg` so that templates written in the language can be used as renderers. See :ref:`adding_and_overriding_renderers` for instructions on how to create your own template renderer and :ref:`available_template_system_bindings` for example packages. If you need more control over the status code and content-type, or other response attributes from views that use direct templating, you may set attributes on the response that influence these values. Here's an example of changing the content-type and status of the response object returned by :func:`repoze.bfg.chameleon_zpt.render_template_to_response`: .. code-block:: python :linenos: from repoze.bfg.chameleon_zpt import render_template_to_response def sample_view(request): response = render_template_to_response('templates/foo.pt', foo=1, bar=2) response.content_type = 'text/plain' response.status_int = 204 return response Here's an example of manufacturing a response object using the result of :func:`repoze.bfg.chameleon_zpt.render_template` (a string): .. code-block:: python :linenos: from repoze.bfg.chameleon_zpt import render_template from webob import Response def sample_view(request): result = render_template('templates/foo.pt', foo=1, bar=2) response = Response(result) response.content_type = 'text/plain' return response .. index:: single: templates used as renderers single: template renderers single: renderer (template) .. _templates_used_as_renderers: Templates Used as Renderers --------------------------- Instead of using templating system APIs within the body of a view function directly to render a specific template, you may associate a template written in a supported templating language with a view indirectly by specifying it as a :term:`renderer`. To use a renderer, specify a template :term:`resource specification` as the ``renderer`` argument or attribute to the :term:`view configuration` of a :term:`view callable`. Then return a *dictionary* from that view callable. The dictionary items returned by the view callable will be made available to the renderer template as top-level names. The association of a template as a renderer for a :term:`view configuration` makes it possible to replace code within a :term:`view callable` that handles the rendering of a template. Here's an example of using a :class:`repoze.bfg.view.bfg_view` decorator to specify a :term:`view configuration` that names a template renderer: .. code-block:: python :linenos: from repoze.bfg.view import bfg_view @bfg_view(renderer='templates/foo.pt') def my_view(request): return {'foo':1, 'bar':2} The ``renderer`` argument to the ``@bfg_view`` configuration decorator shown above is the template *path*. In the example above, the path ``templates/foo.pt`` is *relative*. Relative to what, you ask? Relative to the directory in which the file which defines the view configuration lives. In this case, this is the directory containing the file that defines the ``my_view`` function. Although a renderer path is usually just a simple relative pathname, a path named as a renderer can be absolute, starting with a slash on UNIX or a drive letter prefix on Windows. The path can alternately be a :term:`resource specification` in the form ``some.dotted.package_name:relative/path``, making it possible to address template resources which live in another package. When a template :term:`renderer` is used to render the result of a view callable, several names are passed into the template as top-level names by default, including ``context`` and ``request``. Similar renderer configuration can be done imperatively and via :term:`ZCML`. See :ref:`views_which_use_a_renderer`. See also :ref:`built_in_renderers`. Not just any template from any arbitrary templating system may be used as a renderer. Bindings must exist specifically for :mod:`repoze.bfg` to use a templating language template as a renderer. Currently, :mod:`repoze.bfg` has built-in support for two Chameleon templating languages: ZPT and text. See :ref:`built_in_renderers` for a discussion of their details. :mod:`repoze.bfg` also supports the use of :term:`Jinja2` templates as renderers. See :ref:`available_template_system_bindings`. .. sidebar:: Why Use A Renderer Using a renderer is usually a better way to render templates than using any templating API directly from within a :term:`view callable` because it makes the view callable more unit-testable. Views which use templating APIs directly must return a :term:`Response` object. Making testing assertions about response objects is typically an indirect process, because it means that your test code often needs to somehow parse information out of the response body (often HTML). View callables which use renderers typically return a dictionary, and making assertions about the information is almost always more direct than needing to parse HTML. Specifying a renderer from within :term:`ZCML` (as opposed to imperatively or via a ``bfg_view`` decorator, or using a template directly from within a view callable) also makes it possible for someone to modify the template used to render a view without needing to fork your code to do so. See :ref:`extending_chapter` for more information. By default, views rendered via a template renderer return a :term:`Response` object which has a *status code* of ``200 OK`` and a *content-type* of ``text/html``. To vary attributes of the response of a view that uses a renderer, such as the content-type, headers, or status attributes, you must set attributes on the *request* object within the view before returning the dictionary. See :ref:`response_request_attrs` for more information. .. index:: single: Chameleon ZPT templates single: ZPT templates (Chameleon) .. _chameleon_zpt_templates: :term:`Chameleon` ZPT Templates ------------------------------- Like :term:`Zope`, :mod:`repoze.bfg` uses :term:`ZPT` (Zope Page Templates) as its default templating language. However, :mod:`repoze.bfg` uses a different implementation of the :term:`ZPT` specification than Zope does: the :term:`Chameleon` templating engine. The Chameleon engine complies largely with the `Zope Page Template `_ template specification. However, it is significantly faster. The language definition documentation for Chameleon ZPT-style templates is available from `the Chameleon website `_. .. warning:: :term:`Chameleon` only works on :term:`CPython` platforms and :term:`Google App Engine`. On :term:`Jython` and other non-CPython platforms, you should use ``repoze.bfg.jinja2`` instead. See :ref:`available_template_system_bindings`. Given that there is a :term:`Chameleon` ZPT template named ``foo.pt`` in a directory in your application named ``templates``, you can render the template as a :term:`renderer` like so: .. code-block:: python :linenos: from repoze.bfg.view import bfg_view @bfg_view(renderer='templates/foo.pt') def my_view(request): return {'foo':1, 'bar':2} If you'd rather use templates directly within a view callable (without the indirection of using a renderer), see :ref:`chameleon_zpt_module` for the API description. See also :ref:`built_in_renderers` for more general information about renderers, including Chameleon ZPT renderers. .. index:: single: sample template A Sample ZPT Template ~~~~~~~~~~~~~~~~~~~~~ Here's what a simple :term:`Chameleon` ZPT template used under :mod:`repoze.bfg` might look like: .. code-block:: xml :linenos: ${project} Application

Welcome to ${project}, an application generated by the repoze.bfg web application framework.

Note the use of :term:`Genshi` -style ``${replacements}`` above. This is one of the ways that :term:`Chameleon` ZPT differs from standard ZPT. The above template expects to find a ``project`` key in the set of keywords passed in to it via :func:`repoze.bfg.chameleon_zpt.render_template` or :func:`repoze.bfg.render_template_to_response`. Typical ZPT attribute-based syntax (e.g. ``tal:content`` and ``tal:replace``) also works in these templates. .. index:: single: ZPT macros single: Chameleon ZPT macros Using ZPT Macros in :mod:`repoze.bfg` ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When a :term:`renderer` is used to render a template, :mod:`repoze.bfg` makes at least two top-level names available to the template by default: ``context`` and ``request``. One of the common needs in ZPT-based templates is to use one template's "macros" from within a different template. In Zope, this is typically handled by retrieving the template from the ``context``. But having a hold of the context in :mod:`repoze.bfg` is not helpful: templates cannot usually be retrieved from models. To use macros in :mod:`repoze.bfg`, you need to make the macro template itself available to the rendered template by passing the template in which the macro is defined (or even the macro itself) *into* the rendered template. To make a macro available to the rendered template, you can retrieve a different template using the :func:`repoze.bfg.chameleon_zpt.get_template` API, and pass it in to the template being rendered. For example, using a :term:`view configuration` via a :class:`repoze.bfg.view.bfg_view` decorator that uses a :term:`renderer`: .. code-block:: python :linenos: from repoze.bfg.chameleon_zpt import get_template from repoze.bfg.view import bfg_view @bfg_view(renderer='templates/mytemplate.pt') def my_view(request): main = get_template('templates/master.pt') return {'main':main} Where ``templates/master.pt`` might look like so: .. code-block:: xml :linenos:

Hello Fred!

And ``templates/mytemplate.pt`` might look like so: .. code-block:: xml :linenos: Chris .. index:: single: Chameleon text templates .. _chameleon_text_templates: Templating with :term:`Chameleon` Text Templates ------------------------------------------------ :mod:`repoze.bfg` also allows for the use of templates which are composed entirely of non-XML text via :term:`Chameleon`. To do so, you can create templates that are entirely composed of text except for ``${name}`` -style substitution points. Here's an example usage of a Chameleon text template. Create a file on disk named ``mytemplate.txt`` in your project's ``templates`` directory with the following contents:: Hello, ${name}! Then in your project's ``views.py`` module, you can create a view which renders this template: .. code-block:: python :linenos: from repoze.bfg.chameleon_zpt import get_template from repoze.bfg.view import bfg_view @bfg_view(renderer='templates/mytemplate.txt') def my_view(request): return {'name':'world'} When the template is rendered, it will show: .. code-block:: text Hello, world! If you'd rather use templates directly within a view callable (without the indirection of using a renderer), see :ref:`chameleon_text_module` for the API description. See also :ref:`built_in_renderers` for more general information about renderers, including Chameleon text renderers. .. index:: single: template renderer side effects Side Effects of Rendering a Chameleon Template ---------------------------------------------- When a Chameleon template is rendered from a file, the templating engine writes a file in the same directory as the template file itself as a kind of cache, in order to do less work the next time the template needs to be read from disk. If you see "strange" ``.py`` files showing up in your ``templates`` directory (or otherwise directly "next" to your templates), it is due to this feature. If you're using a version control system such as Subversion, you should cause it to ignore these files. Here's the contents of the author's ``svn propedit svn:ignore .`` in each of my ``templates`` directories. .. code-block:: bash :linenos: *.pt.py *.txt.py Note that I always name my Chameleon ZPT template files with a ``.pt`` extension and my Chameleon text template files with a ``.txt`` extension so that these ``svn:ignore`` patterns work. .. index:: single: automatic reloading of templates single: template automatic reload .. _reload_templates_section: Automatically Reloading Templates --------------------------------- It's often convenient to see changes you make to a template file appear immediately without needing to restart the application process. :mod:`repoze.bfg` allows you to configure your application development environment so that a change to a template will be automatically detected, and the template will be reloaded on the next rendering. .. warning:: auto-template-reload behavior is not recommended for production sites as it slows rendering slightly; it's usually only desirable during development. In order to turn on automatic reloading of templates, you can use an environment variable setting or a configuration file setting. To use an environment variable, start your application under a shell using the ``BFG_RELOAD_TEMPLATES`` operating system environment variable set to ``1``, For example:: $ BFG_RELOAD_TEMPLATES=1 bin/paster serve myproject.ini To use a setting in the application ``.ini`` file for the same purpose, set the ``reload_templates`` key to ``true`` within the application's configuration section, e.g.:: [app:main] use = egg:MyProject#app reload_templates = true .. index:: single: template internationalization single: internationalization (of templates) :term:`Chameleon` Template Internationalization ----------------------------------------------- See `the internationalization chapter `_ of the Chameleon documentation for information about supporting internationalized units of text within :term:`Chameleon` templates. .. index:: single: template system bindings single: Jinja2 .. _available_template_system_bindings: Available Add-On Template System Bindings ----------------------------------------- Jinja2 template bindings are available for :mod:`repoze.bfg` in the ``repoze.bfg.jinja2`` package. It lives in the Repoze Subversion repository at `http://svn.repoze.org/repoze.bfg.jinja2 `_; it is also available from :term:`PyPI`.