Defining Views

A view callable in a traversal -based Pyramid application is typically a simple Python function that accepts two parameters: context and request. A view callable is assumed to return a response object.

Note

A Pyramid view can also be defined as callable which accepts only a request argument. You'll see this one-argument pattern used in other Pyramid tutorials and applications. Either calling convention will work in any Pyramid application; the calling conventions can be used interchangeably as necessary. In traversal based applications, URLs are mapped to a context resource, and since our resource tree also represents our application's "domain model", we're often interested in the context because it represents the persistent storage of our application. For this reason, in this tutorial we define views as callables that accept context in the callable argument list. If you do need the context within a view function that only takes the request as a single argument, you can obtain it via request.context.

We're going to define several view callable functions, then wire them into Pyramid using some view configuration.

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:

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import os

from setuptools import setup, find_packages

here = os.path.abspath(os.path.dirname(__file__))
with open(os.path.join(here, 'README.txt')) as f:
    README = f.read()
with open(os.path.join(here, 'CHANGES.txt')) as f:
    CHANGES = f.read()

requires = [
    'pyramid',
    'pyramid_chameleon',
    'pyramid_debugtoolbar',
    'pyramid_tm',
    'pyramid_zodbconn',
    'transaction',
    'ZODB3',
    'waitress',
    'docutils',
    ]

setup(name='tutorial',
      version='0.0',
      description='tutorial',
      long_description=README + '\n\n' + CHANGES,
      classifiers=[
        "Programming Language :: Python",
        "Framework :: Pyramid",
        "Topic :: Internet :: WWW/HTTP",
        "Topic :: Internet :: WWW/HTTP :: WSGI :: Application",
        ],
      author='',
      author_email='',
      url='',
      keywords='web pylons pyramid',
      packages=find_packages(),
      include_package_data=True,
      zip_safe=False,
      install_requires=requires,
      tests_require=requires,
      test_suite="tutorial",
      entry_points="""\
      [paste.app_factory]
      main = tutorial:main
      """,
      )

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:

$ cd tutorial
$ $VENV/bin/python setup.py develop

On Windows:

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:

Finished processing dependencies for tutorial==0.0

Adding view functions in views.py

It's time for a major change. Open tutorial/tutorial/views.py and edit it to look like the following:

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from docutils.core import publish_parts
import re

from pyramid.httpexceptions import HTTPFound
from pyramid.view import view_config

from .models import Page

# regular expression used to find WikiWords
wikiwords = re.compile(r"\b([A-Z]\w+[A-Z]+\w+)")

@view_config(context='.models.Wiki')
def view_wiki(context, request):
    return HTTPFound(location=request.resource_url(context, 'FrontPage'))

@view_config(context='.models.Page', renderer='templates/view.pt')
def view_page(context, request):
    wiki = context.__parent__

    def check(match):
        word = match.group(1)
        if word in wiki:
            page = wiki[word]
            view_url = request.resource_url(page)
            return '<a href="%s">%s</a>' % (view_url, word)
        else:
            add_url = request.application_url + '/add_page/' + word 
            return '<a href="%s">%s</a>' % (add_url, word)

    content = publish_parts(context.data, writer_name='html')['html_body']
    content = wikiwords.sub(check, content)
    edit_url = request.resource_url(context, 'edit_page')
    return dict(page = context, content = content, edit_url = edit_url)

@view_config(name='add_page', context='.models.Wiki',
             renderer='templates/edit.pt')
def add_page(context, request):
    pagename = request.subpath[0]
    if 'form.submitted' in request.params:
        body = request.params['body']
        page = Page(body)
        page.__name__ = pagename
        page.__parent__ = context
        context[pagename] = page
        return HTTPFound(location = request.resource_url(page))
    save_url = request.resource_url(context, 'add_page', pagename)
    page = Page('')
    page.__name__ = pagename
    page.__parent__ = context
    return dict(page = page, save_url = save_url)

@view_config(name='edit_page', context='.models.Page',
             renderer='templates/edit.pt')
def edit_page(context, request):
    if 'form.submitted' in request.params:
        context.data = request.params['body']
        return HTTPFound(location = request.resource_url(context))

    return dict(page=context,
                save_url=request.resource_url(context, 'edit_page'))

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 zodb scaffold. It was only an example and isn't relevant to our application.

Then we added four view callable functions to our views.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 views.py. A project may have many view callables throughout its codebase in arbitrarily named files. Files implementing view callables often have view in their filenames (or may live in a Python subpackage of your application package named views), but this is only by convention.

The view_wiki view function

Following is the code for the view_wiki view function and its decorator:

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@view_config(context='.models.Wiki')
def view_wiki(context, request):
    return HTTPFound(location=request.resource_url(context, 'FrontPage'))

Note

In our code, we use an import that is relative to our package named tutorial, meaning we can omit the name of the package in the import and context statements. In our narrative, however, we refer to a class and thus we use the absolute form, meaning that the name of the package is included.

view_wiki() is the 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".

We provide it with a @view_config decorator which names the class tutorial.models.Wiki as its context. This means that when a Wiki resource is the context and no view name exists in the request, then this view will be used. The view configuration associated with view_wiki does not use a renderer because the view callable always returns a response object rather than a dictionary. No renderer is necessary when a view returns a response object.

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 pyramid.httpexceptions.HTTPFound class (instances of which implement the pyramid.interfaces.IResponse interface, like pyramid.response.Response does). It uses the pyramid.request.Request.route_url() API to construct an URL to the FrontPage page resource (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:

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@view_config(context='.models.Page', renderer='templates/view.pt')
def view_page(context, request):
    wiki = context.__parent__

    def check(match):
        word = match.group(1)
        if word in wiki:
            page = wiki[word]
            view_url = request.resource_url(page)
            return '<a href="%s">%s</a>' % (view_url, word)
        else:
            add_url = request.application_url + '/add_page/' + word 
            return '<a href="%s">%s</a>' % (add_url, word)

    content = publish_parts(context.data, writer_name='html')['html_body']
    content = wikiwords.sub(check, content)
    edit_url = request.resource_url(context, 'edit_page')
    return dict(page = context, content = content, edit_url = edit_url)

The view_page function is configured to respond as the default view of a Page resource. We provide it with a @view_config decorator which names the class tutorial.models.Page as its context. This means that when a Page resource is the context, and no view name exists in the request, this view will be used. We inform Pyramid this view will use the templates/view.pt template file as a renderer.

The view_page function generates the reStructuredText body of a page (stored as the data attribute of the context passed to the view; the context will be a Page resource) 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 (our page's __parent__) already contains a page with the matched WikiWord name, the check function 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, the function 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 resource.

We then generate an edit URL because it's easier to do here than in the template, and we wrap up a number of arguments in a dictionary and return it.

The arguments we wrap into a dictionary include page, content, and edit_url. As a result, the template associated with this view callable (via renderer= in its configuration) will be able to use these names to perform various rendering tasks. The template associated with this view callable will be a template which lives in templates/view.pt.

Note the contrast between this view callable and the view_wiki view callable. In the view_wiki view callable, we unconditionally return a response object. In the view_page view callable, we return a dictionary. It is always fine to return a response object from a Pyramid view. Returning a dictionary is allowed only when there is a renderer associated with the view callable in the view configuration.

The add_page view function

Here is the code for the add_page view function and its decorator:

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@view_config(name='add_page', context='.models.Wiki',
             renderer='templates/edit.pt')
def add_page(context, request):
    pagename = request.subpath[0]
    if 'form.submitted' in request.params:
        body = request.params['body']
        page = Page(body)
        page.__name__ = pagename
        page.__parent__ = context
        context[pagename] = page
        return HTTPFound(location = request.resource_url(page))
    save_url = request.resource_url(context, 'add_page', pagename)
    page = Page('')
    page.__name__ = pagename
    page.__parent__ = context
    return dict(page = page, save_url = save_url)

The add_page function is configured to respond when the context resource is a Wiki and the view name is add_page. We provide it with a @view_config decorator which names the string add_page as its view name (via name=), the class tutorial.models.Wiki as its context, and the renderer named templates/edit.pt. This means that when a Wiki resource is the context, and a view name named add_page exists as the result of traversal, this view will be used. We inform Pyramid this view will use the templates/edit.pt template file as a renderer. We share the same template between add and edit views, thus edit.pt instead of add.pt.

The add_page function will be 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. It also acts as a handler for the form that is generated when we want to add a page resource. The context of the add_page view is always a Wiki resource (not a Page resource).

The request subpath in Pyramid is the sequence of names that are found after the view name in the URL segments given in the PATH_INFO of the WSGI request as the result of traversal. If our add view is invoked via, e.g., http://localhost:6543/add_page/SomeName, the subpath will be a tuple: ('SomeName',).

The add view takes the zeroth element of the subpath (the wiki page name), and aliases it to the name attribute in order to know the name of the page we're trying to add.

If the view rendering is not a result of a form submission (if the expression 'form.submitted' in request.params is False), the view 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 trying to use the same template (templates/edit.pt) for the add view as well as the page edit view. To do so, we create a dummy Page resource object in order to satisfy the edit form's desire to have some page object exposed as page, and we'll render the template to a response.

If the view rendering is a result of a form submission (if the expression 'form.submitted' in request.params is True), we grab the page body from the form data, create a Page object using the name in the subpath and the page body, and save it into "our context" (the Wiki) using the __setitem__ method of the context. We then redirect back to the view_page view (the default view for a page) for the newly created page.

The edit_page view function

Here is the code for the edit_page view function and its decorator:

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@view_config(name='edit_page', context='.models.Page',
             renderer='templates/edit.pt')
def edit_page(context, request):
    if 'form.submitted' in request.params:
        context.data = request.params['body']
        return HTTPFound(location = request.resource_url(context))

    return dict(page=context,
                save_url=request.resource_url(context, 'edit_page'))

The edit_page function is configured to respond when the context is a Page resource and the view name is edit_page. We provide it with a @view_config decorator which names the string edit_page as its view name (via name=), the class tutorial.models.Page as its context, and the renderer named templates/edit.pt. This means that when a Page resource is the context, and a view name exists as the result of traversal named edit_page, this view will be used. We inform Pyramid this view will use the templates/edit.pt template file as a renderer.

The edit_page function will be 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 form post view callable for the form it renders. The context of the edit_page view will always be a Page resource (never a Wiki resource).

If the view execution is not a result of a form submission (if the expression 'form.submitted' in request.params is False), the view simply renders the edit form, passing the page resource, and a save_url which will be used as the action of the generated form.

If the view execution is a result of a form submission (if the expression 'form.submitted' in request.params is True), the view grabs the body element of the request parameter and sets it as the data attribute of the page context. It then redirects to the default view of the context (the page), which will always be the view_page view.

Adding templates

The view_page, add_page and edit_page views that we've added reference a template. Each template is a Chameleon ZPT template. These templates will live in the templates directory of our tutorial package. Chameleon templates must have a .pt extension to be recognized as such.

The view.pt template

Create tutorial/tutorial/templates/view.pt and add the following content:

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<!DOCTYPE html>
<html lang="${request.locale_name}">
  <head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="description" content="pyramid web application">
    <meta name="author" content="Pylons Project">
    <link rel="shortcut icon" href="${request.static_url('tutorial:static/pyramid-16x16.png')}">

    <title>${page.name} - Pyramid tutorial wiki (based on
    TurboGears 20-Minute Wiki)</title>

    <!-- Bootstrap core CSS -->
    <link href="//oss.maxcdn.com/libs/twitter-bootstrap/3.0.3/css/bootstrap.min.css" rel="stylesheet">

    <!-- Custom styles for this scaffold -->
    <link href="${request.static_url('tutorial:static/theme.css')}" rel="stylesheet">

    <!-- HTML5 shim and Respond.js IE8 support of HTML5 elements and media queries -->
    <!--[if lt IE 9]>
      <script src="//oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js"></script>
      <script src="//oss.maxcdn.com/libs/respond.js/1.3.0/respond.min.js"></script>
    <![endif]-->
  </head>
  <body>

    <div class="starter-template">
      <div class="container">
        <div class="row">
          <div class="col-md-2">
            <img class="logo img-responsive" src="${request.static_url('tutorial:static/pyramid.png')}" alt="pyramid web framework">
          </div>
          <div class="col-md-10">
            <div class="content">
              <div tal:replace="structure content">
                Page text goes here.
              </div>
              <p>
                <a tal:attributes="href edit_url" href="">
                  Edit this page
                </a>
              </p>
              <p>
                  Viewing <strong><span tal:replace="page.__name__">
                  Page Name Goes Here</span></strong>
              </p>
              <p>You can return to the
                <a href="${request.application_url}">FrontPage</a>.
              </p>
            </div>
          </div>
        </div>
        <div class="row">
          <div class="copyright">
            Copyright &copy; Pylons Project
          </div>
        </div>
      </div>
    </div>


    <!-- Bootstrap core JavaScript
    ================================================== -->
    <!-- Placed at the end of the document so the pages load faster -->
    <script src="//oss.maxcdn.com/libs/jquery/1.10.2/jquery.min.js"></script>
    <script src="//oss.maxcdn.com/libs/twitter-bootstrap/3.0.3/js/bootstrap.min.js"></script>
  </body>
</html>

This template is used by view_page() for displaying a single wiki page. It includes:

  • A div element that is replaced with the content value provided by the view (lines 36-38). content contains HTML, so the structure keyword is used to prevent escaping it (i.e., changing ">" to "&gt;", etc.)
  • A link that points at the "edit" URL which invokes the edit_page view for the page being viewed (lines 40-42).

The edit.pt template

Create tutorial/tutorial/templates/edit.pt and add the following content:

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<!DOCTYPE html>
<html lang="${request.locale_name}">
  <head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="description" content="pyramid web application">
    <meta name="author" content="Pylons Project">
    <link rel="shortcut icon" href="${request.static_url('tutorial:static/pyramid-16x16.png')}">

    <title>${page.__name__} - Pyramid tutorial wiki (based on
    TurboGears 20-Minute Wiki)</title>

    <!-- Bootstrap core CSS -->
    <link href="//oss.maxcdn.com/libs/twitter-bootstrap/3.0.3/css/bootstrap.min.css" rel="stylesheet">

    <!-- Custom styles for this scaffold -->
    <link href="${request.static_url('tutorial:static/theme.css')}" rel="stylesheet">

    <!-- HTML5 shim and Respond.js IE8 support of HTML5 elements and media queries -->
    <!--[if lt IE 9]>
      <script src="//oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js"></script>
      <script src="//oss.maxcdn.com/libs/respond.js/1.3.0/respond.min.js"></script>
    <![endif]-->
  </head>
  <body>

    <div class="starter-template">
      <div class="container">
        <div class="row">
          <div class="col-md-2">
            <img class="logo img-responsive" src="${request.static_url('tutorial:static/pyramid.png')}" alt="pyramid web framework">
          </div>
          <div class="col-md-10">
            <div class="content">
              <p>
                  Editing <strong><span tal:replace="page.__name__">
                  Page Name Goes Here</span></strong>
              </p>
              <p>You can return to the
                <a href="${request.application_url}">FrontPage</a>.
              </p>
              <form action="${save_url}" method="post">
                <div class="form-group">
                  <textarea class="form-control" name="body" tal:content="page.data" rows="10" cols="60"></textarea>
                </div>
                <div class="form-group">
                  <button type="submit" name="form.submitted" value="Save" class="btn btn-default">Save</button>
                </div>
              </form>
            </div>
          </div>
        </div>
        <div class="row">
          <div class="copyright">
            Copyright &copy; Pylons Project
          </div>
        </div>
      </div>
    </div>


    <!-- Bootstrap core JavaScript
    ================================================== -->
    <!-- Placed at the end of the document so the pages load faster -->
    <script src="//oss.maxcdn.com/libs/jquery/1.10.2/jquery.min.js"></script>
    <script src="//oss.maxcdn.com/libs/twitter-bootstrap/3.0.3/js/bootstrap.min.js"></script>
  </body>
</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:

  • A 10 row by 60 column textarea field named body that is filled with any existing page data when it is rendered (line 45).
  • A submit button that has the name form.submitted (line 48).

The form POSTs back to the save_url argument supplied by the view (line 43). The view will use the body and form.submitted values.

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 System Values Used During Rendering 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.

Viewing the application in a browser

We can finally examine our application in a browser (See Start the application). Launch a browser and visit each of the following URLs, checking that the result is as expected: