============== Defining Views ============== A :term:`view callable` in a :app:`Pyramid` application is typically a simple Python function that accepts a single parameter named :term:`request`. A view callable is assumed to return a :term:`response` object. The request object has a dictionary as an attribute named ``matchdict``. A ``matchdict`` maps the placeholders in the matching URL ``pattern`` to the substrings of the path in the :term:`request` URL. For instance, if a call to :meth:`pyramid.config.Configurator.add_route` has the pattern ``/{one}/{two}``, and a user visits ``http://example.com/foo/bar``, our pattern would be matched against ``/foo/bar`` and the ``matchdict`` would look like ``{'one':'foo', 'two':'bar'}``. Declaring dependencies in our ``setup.py`` file =============================================== The view code in our application will depend on a package which is not a dependency of the original "tutorial" application. The original "tutorial" application was generated by the ``pcreate`` command; it doesn't know about our custom application requirements. We need to add a dependency on the ``docutils`` package to our ``tutorial`` package's ``setup.py`` file by assigning this dependency to the ``requires`` parameter in the ``setup()`` function. Open ``tutorial/setup.py`` and edit it to look like the following: .. literalinclude:: src/views/setup.py :linenos: :emphasize-lines: 20 :language: python Only the highlighted line needs to be added. Running ``setup.py develop`` ============================ Since a new software dependency was added, you will need to run ``python setup.py develop`` again inside the root of the ``tutorial`` package to obtain and register the newly added dependency distribution. Make sure your current working directory is the root of the project (the directory in which ``setup.py`` lives) and execute the following command. On UNIX: .. code-block:: bash $ cd tutorial $ $VENV/bin/python setup.py develop On Windows: .. code-block:: text c:\pyramidtut> cd tutorial c:\pyramidtut\tutorial> %VENV%\Scripts\python setup.py develop Success executing this command will end with a line to the console something like this:: Finished processing dependencies for tutorial==0.0 Adding view functions in ``views/default.py`` ============================================= It's time for a major change. Open ``tutorial/views/default.py`` and edit it to look like the following: .. literalinclude:: src/views/tutorial/views/default.py :linenos: :language: python :emphasize-lines: 1-9,12-68 The highlighted lines need to be added or edited. We added some imports, and created a regular expression to find "WikiWords". We got rid of the ``my_view`` view function and its decorator that was added when we originally rendered the ``alchemy`` scaffold. It was only an example and isn't relevant to our application. We also delated the ``db_err_msg`` string. Then we added four :term:`view callable` functions to our ``views/default.py`` module: * ``view_wiki()`` - Displays the wiki itself. It will answer on the root URL. * ``view_page()`` - Displays an individual page. * ``add_page()`` - Allows the user to add a page. * ``edit_page()`` - Allows the user to edit a page. We'll describe each one briefly in the following sections. .. note:: There is nothing special about the filename ``default.py`` exept that it is a Python module. A project may have many view callables throughout its codebase in arbitrarily named modules. Modules implementing view callables often have ``view`` in their name (or may live in a Python subpackage of your application package named ``views``, as in our case), but this is only by convention, not a requirement. The ``view_wiki`` view function ------------------------------- Following is the code for the ``view_wiki`` view function and its decorator: .. literalinclude:: src/views/tutorial/views/default.py :lines: 17-20 :lineno-match: :linenos: :language: python ``view_wiki()`` is the :term:`default view` that gets called when a request is made to the root URL of our wiki. It always redirects to an URL which represents the path to our "FrontPage". The ``view_wiki`` view callable always redirects to the URL of a Page resource named "FrontPage". To do so, it returns an instance of the :class:`pyramid.httpexceptions.HTTPFound` class (instances of which implement the :class:`pyramid.interfaces.IResponse` interface, like :class:`pyramid.response.Response` does). It uses the :meth:`pyramid.request.Request.route_url` API to construct an URL to the ``FrontPage`` page (i.e., ``http://localhost:6543/FrontPage``), and uses it as the "location" of the ``HTTPFound`` response, forming an HTTP redirect. The ``view_page`` view function ------------------------------- Here is the code for the ``view_page`` view function and its decorator: .. literalinclude:: src/views/tutorial/views/default.py :lines: 22-42 :lineno-match: :linenos: :language: python ``view_page()`` is used to display a single page of our wiki. It renders the :term:`reStructuredText` body of a page (stored as the ``data`` attribute of a ``Page`` model object) as HTML. Then it substitutes an HTML anchor for each *WikiWord* reference in the rendered HTML using a compiled regular expression. The curried function named ``check`` is used as the first argument to ``wikiwords.sub``, indicating that it should be called to provide a value for each WikiWord match found in the content. If the wiki already contains a page with the matched WikiWord name, ``check()`` generates a view link to be used as the substitution value and returns it. If the wiki does not already contain a page with the matched WikiWord name, ``check()`` generates an "add" link as the substitution value and returns it. As a result, the ``content`` variable is now a fully formed bit of HTML containing various view and add links for WikiWords based on the content of our current page object. We then generate an edit URL because it's easier to do here than in the template, and we return a dictionary with a number of arguments. The fact that ``view_page()`` returns a dictionary (as opposed to a :term:`response` object) is a cue to :app:`Pyramid` that it should try to use a :term:`renderer` associated with the view configuration to render a response. In our case, the renderer used will be the ``view.jinja2`` template, as indicated in the ``@view_config`` decorator that is applied to ``view_page()``. The ``add_page`` view function ------------------------------ Here is the code for the ``add_page`` view function and its decorator: .. literalinclude:: src/views/tutorial/views/default.py :lines: 44-55 :lineno-match: :linenos: :language: python ``add_page()`` is invoked when a user clicks on a *WikiWord* which isn't yet represented as a page in the system. The ``check`` function within the ``view_page`` view generates URLs to this view. ``add_page()`` also acts as a handler for the form that is generated when we want to add a page object. The ``matchdict`` attribute of the request passed to the ``add_page()`` view will have the values we need to construct URLs and find model objects. The ``matchdict`` will have a ``'pagename'`` key that matches the name of the page we'd like to add. If our add view is invoked via, e.g., ``http://localhost:6543/add_page/SomeName``, the value for ``'pagename'`` in the ``matchdict`` will be ``'SomeName'``. If the view execution *is* a result of a form submission (i.e., the expression ``'form.submitted' in request.params`` is ``True``), we grab the page body from the form data, create a Page object with this page body and the name taken from ``matchdict['pagename']``, and save it into the database using ``request.dbession.add``. We then redirect back to the ``view_page`` view for the newly created page. If the view execution is *not* a result of a form submission (i.e., the expression ``'form.submitted' in request.params`` is ``False``), the view callable renders a template. To do so, it generates a ``save_url`` which the template uses as the form post URL during rendering. We're lazy here, so we're going to use the same template (``templates/edit.jinja2``) for the add view as well as the page edit view. To do so we create a dummy ``Page`` object in order to satisfy the edit form's desire to have *some* page object exposed as ``page``. :app:`Pyramid` will render the template associated with this view to a response. The ``edit_page`` view function ------------------------------- Here is the code for the ``edit_page`` view function and its decorator: .. literalinclude:: src/views/tutorial/views/default.py :lines: 57-68 :lineno-match: :linenos: :language: python ``edit_page()`` is invoked when a user clicks the "Edit this Page" button on the view form. It renders an edit form, but it also acts as the handler for the form it renders. The ``matchdict`` attribute of the request passed to the ``edit_page`` view will have a ``'pagename'`` key matching the name of the page the user wants to edit. If the view execution *is* a result of a form submission (i.e., the expression ``'form.submitted' in request.params`` is ``True``), the view grabs the ``body`` element of the request parameters and sets it as the ``data`` attribute of the page object. It then redirects to the ``view_page`` view of the wiki page. If the view execution is *not* a result of a form submission (i.e., the expression ``'form.submitted' in request.params`` is ``False``), the view simply renders the edit form, passing the page object and a ``save_url`` which will be used as the action of the generated form. Adding templates ================ The ``view_page``, ``add_page`` and ``edit_page`` views that we've added reference a :term:`template`. Each template is a :term:`Jinja2` template. These templates will live in the ``templates`` directory of our tutorial package. Jinja2 templates must have a ``.jinja2`` extension to be recognized as such. The ``layout.jinja2`` template ------------------------------ Replace ``tutorial/templates/layout.jinja2`` with the following content: .. literalinclude:: src/views/tutorial/templates/layout.jinja2 :linenos: :emphasize-lines: 11,36 :language: html Since we're using a templating engine we can factor common boilerplate out of our page templates into reusable components. One method for doing this is template inheritance via blocks. - We have defined 2 placeholders in the layout template where a child template can override the content. These blocks are named ``title`` (line 11) and ``content`` (line 36). - Please refer to the Jinja2_ documentation for more information about template inheritance. The ``view.jinja2`` template ---------------------------- Create ``tutorial/templates/view.jinja2`` and add the following content: .. literalinclude:: src/views/tutorial/templates/view.jinja2 :linenos: :emphasize-lines: 1,4,6-8 :language: html This template is used by ``view_page()`` for displaying a single wiki page. It includes: - We begin by extending the ``layout.jinja2`` template defined above which provides the skeleton of the page (line 1). - We override the ``content`` block from the base layout to insert our markup into the body (line 3). - A variable that is replaced with the ``content`` value provided by the view (line 4). ``content`` contains HTML, so the ``|safe`` filter is used to prevent escaping it (e.g., changing ">" to ">"). - A link that points at the "edit" URL which invokes the ``edit_page`` view for the page being viewed (lines 6-8). The ``edit.jinja2`` template ---------------------------- Create ``tutorial/templates/edit.jinja2`` and add the following content: .. literalinclude:: src/views/tutorial/templates/edit.jinja2 :linenos: :emphasize-lines: 3,12,14,17 :language: html This template is used by ``add_page()`` and ``edit_page()`` for adding and editing a wiki page. It displays a page containing a form that includes: - Again we are extending the ``layout.jinja2`` template which provides the skeleton of the page. - Override the ``title`` block to affect the ```` tag in the ``head`` of the page (line 3). - A 10-row by 60-column ``textarea`` field named ``body`` that is filled with any existing page data when it is rendered (line 14). - A submit button that has the name ``form.submitted`` (line 17). The form POSTs back to the ``save_url`` argument supplied by the view (line 12). The view will use the ``body`` and ``form.submitted`` values. The ``404.jinja2`` template --------------------------- Replace ``tutorial/templates/404.jinja2`` with the following content: .. literalinclude:: src/views/tutorial/templates/404.jinja2 :linenos: :language: html This template is linked from the ``notfound_view`` defined in ``tutorial/views/notfound.py`` as shown here: .. literalinclude:: src/views/tutorial/views/notfound.py :linenos: :language: python There are several important things to note about this configuration: - The ``notfound_view`` in the above snippet is called an :term:`exception view`. For more information see :ref:`special_exceptions_in_callables`. - The ``notfound_view`` sets the response status to 404. It's possible to affect the response object used by the renderer via :ref:`request_response_attr`. - The ``notfound_view`` is registered as an exception view and will be invoked **only** if ``pyramid.httpexceptions.HTTPNotFound`` is raised as an exception. This means it will not be invoked for any responses returned from a view normally. For example, on line 27 of ``tutorial/views/default.py`` the exception is raised which will trigger the view. Finally, you may delete the ``tutorial/templates/mytemplate.jinja2`` template that was provided by the ``alchemy`` scaffold as we have created our own templates for the wiki. .. note:: Our templates use a ``request`` object that none of our tutorial views return in their dictionary. ``request`` is one of several names that are available "by default" in a template when a template renderer is used. See :ref:`renderer_system_values` for information about other names that are available by default when a template is used as a renderer. Static assets ------------- Our templates name static assets, including CSS and images. We don't need to create these files within our package's ``static`` directory because they were provided at the time we created the project. As an example, the CSS file will be accessed via ``http://localhost:6543/static/theme.css`` by virtue of the call to the ``add_static_view`` directive we've made in the ``__init__.py`` file. Any number and type of static assets can be placed in this directory (or subdirectories) and are just referred to by URL or by using the convenience method ``static_url``, e.g., ``request.static_url('<package>:static/foo.css')`` within templates. Adding routes to ``__init__.py`` ================================ The ``__init__.py`` file contains :meth:`pyramid.config.Configurator.add_route` calls which serve to add routes to our application. First, we’ll get rid of the existing route created by the template using the name ``'home'``. It’s only an example and isn’t relevant to our application. We then need to add four calls to ``add_route``. Note that the *ordering* of these declarations is very important. ``route`` declarations are matched in the order they're found in the ``__init__.py`` file. #. Add a declaration which maps the pattern ``/`` (signifying the root URL) to the route named ``view_wiki``. It maps to our ``view_wiki`` view callable by virtue of the ``@view_config`` attached to the ``view_wiki`` view function indicating ``route_name='view_wiki'``. #. Add a declaration which maps the pattern ``/{pagename}`` to the route named ``view_page``. This is the regular view for a page. It maps to our ``view_page`` view callable by virtue of the ``@view_config`` attached to the ``view_page`` view function indicating ``route_name='view_page'``. #. Add a declaration which maps the pattern ``/add_page/{pagename}`` to the route named ``add_page``. This is the add view for a new page. It maps to our ``add_page`` view callable by virtue of the ``@view_config`` attached to the ``add_page`` view function indicating ``route_name='add_page'``. #. Add a declaration which maps the pattern ``/{pagename}/edit_page`` to the route named ``edit_page``. This is the edit view for a page. It maps to our ``edit_page`` view callable by virtue of the ``@view_config`` attached to the ``edit_page`` view function indicating ``route_name='edit_page'``. As a result of our edits, the ``__init__.py`` file should look something like: .. literalinclude:: src/views/tutorial/__init__.py :linenos: :emphasize-lines: 11-14 :language: python The highlighted lines are the ones that need to be added or edited. Viewing the application in a browser ==================================== We can finally examine our application in a browser (See :ref:`wiki2-start-the-application`). Launch a browser and visit each of the following URLs, checking that the result is as expected: - http://localhost:6543/ invokes the ``view_wiki`` view. This always redirects to the ``view_page`` view of the ``FrontPage`` page object. - http://localhost:6543/FrontPage invokes the ``view_page`` view of the front page object. - http://localhost:6543/FrontPage/edit_page invokes the edit view for the front page object. - http://localhost:6543/add_page/SomePageName invokes the add view for a page. - To generate an error, visit http://localhost:6543/foobars/edit_page which will generate a ``NoResultFound: No row was found for one()`` error. You'll see an interactive traceback facility provided by :term:`pyramid_debugtoolbar`. .. _jinja2: http://jinja.pocoo.org/