Defining Views¶
A view callable in a Pyramid application is typically a simple Python function that accepts a single parameter named request. A view callable is assumed to return a response object.
The request object passed to every view that is called as the result of a
route match has an attribute named matchdict
that contains the elements
placed into the URL by the pattern
of a route
statement. For
instance, if a call to pyramid.config.Configurator.add_route()
in
__init__.py
had the pattern {one}/{two}
, and the URL at
http://example.com/foo/bar
was invoked, matching this pattern, the
matchdict
dictionary attached to the request passed to the view would
have a 'one'
key with the value 'foo'
and a 'two'
key with the
value 'bar'
.
The source code for this tutorial stage can be browsed at http://github.com/Pylons/pyramid/tree/1.3-branch/docs/tutorials/wiki2/src/views/.
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 setup()
.
Open tutorial/setup.py
and edit it to look like the following:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 | import os
from setuptools import setup, find_packages
here = os.path.abspath(os.path.dirname(__file__))
README = open(os.path.join(here, 'README.txt')).read()
CHANGES = open(os.path.join(here, 'CHANGES.txt')).read()
requires = [
'pyramid',
'SQLAlchemy',
'transaction',
'pyramid_tm',
'pyramid_debugtoolbar',
'zope.sqlalchemy',
'waitress',
'docutils',
]
setup(name='tutorial',
version='0.0',
description='tutorial',
long_description=README + '\n\n' + CHANGES,
classifiers=[
"Programming Language :: Python",
"Framework :: Pylons",
"Topic :: Internet :: WWW/HTTP",
"Topic :: Internet :: WWW/HTTP :: WSGI :: Application",
],
author='',
author_email='',
url='',
keywords='web wsgi bfg pylons pyramid',
packages=find_packages(),
include_package_data=True,
zip_safe=False,
test_suite='tutorial',
install_requires = requires,
entry_points = """\
[paste.app_factory]
main = tutorial:main
[console_scripts]
initialize_tutorial_db = tutorial.scripts.initializedb:main
""",
)
|
(Only the highlighted line needs to be added.)
Running setup.py develop
¶
Since a new software dependency was added, you will need to rerun python
setup.py develop
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
$ ../bin/python setup.py develop
On Windows:
c:\pyramidtut> cd tutorial
c:\pyramidtut\tutorial> ..\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
Changing the views.py
File¶
It’s time for a major change. Open tutorial/tutorial/views.py
and edit it to look like the following:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 | import re
from docutils.core import publish_parts
from pyramid.httpexceptions import (
HTTPFound,
HTTPNotFound,
)
from pyramid.view import view_config
from .models import (
DBSession,
Page,
)
# regular expression used to find WikiWords
wikiwords = re.compile(r"\b([A-Z]\w+[A-Z]+\w+)")
@view_config(route_name='view_wiki')
def view_wiki(request):
return HTTPFound(location = request.route_url('view_page',
pagename='FrontPage'))
@view_config(route_name='view_page', renderer='templates/view.pt')
def view_page(request):
pagename = request.matchdict['pagename']
page = DBSession.query(Page).filter_by(name=pagename).first()
if page is None:
return HTTPNotFound('No such page')
def check(match):
word = match.group(1)
exists = DBSession.query(Page).filter_by(name=word).all()
if exists:
view_url = request.route_url('view_page', pagename=word)
return '<a href="%s">%s</a>' % (view_url, word)
else:
add_url = request.route_url('add_page', pagename=word)
return '<a href="%s">%s</a>' % (add_url, word)
content = publish_parts(page.data, writer_name='html')['html_body']
content = wikiwords.sub(check, content)
edit_url = request.route_url('edit_page', pagename=pagename)
return dict(page=page, content=content, edit_url=edit_url)
@view_config(route_name='add_page', renderer='templates/edit.pt')
def add_page(request):
name = request.matchdict['pagename']
if 'form.submitted' in request.params:
body = request.params['body']
page = Page(name, body)
DBSession.add(page)
return HTTPFound(location = request.route_url('view_page',
pagename=name))
save_url = request.route_url('add_page', pagename=name)
page = Page('', '')
return dict(page=page, save_url=save_url)
@view_config(route_name='edit_page', renderer='templates/edit.pt')
def edit_page(request):
name = request.matchdict['pagename']
page = DBSession.query(Page).filter_by(name=name).one()
if 'form.submitted' in request.params:
page.data = request.params['body']
DBSession.add(page)
return HTTPFound(location = request.route_url('view_page',
pagename=name))
return dict(
page=page,
save_url = request.route_url('edit_page', pagename=name),
)
|
(The highlighted lines are the ones that need to be added or edited.)
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.
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 and show the resulting views.py
file
afterward.
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¶
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
a URL which represents the path to our “FrontPage”.
1 2 3 4 | @view_config(route_name='view_wiki')
def view_wiki(request):
return HTTPFound(location = request.route_url('view_page',
pagename='FrontPage'))
|
view_wiki()
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 a
URL to the FrontPage
page (e.g. http://localhost:6543/FrontPage
), which
is used as the “location” of the HTTPFound response, forming an HTTP redirect.
The view_page
view function¶
view_page()
is used to display a single page of our
wiki. It renders the ReStructuredText body of a page (stored as
the data
attribute of a Page object) as HTML. Then it substitutes an
HTML anchor for each WikiWord reference in the rendered HTML using a
compiled regular expression.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | @view_config(route_name='view_page', renderer='templates/view.pt')
def view_page(request):
pagename = request.matchdict['pagename']
page = DBSession.query(Page).filter_by(name=pagename).first()
if page is None:
return HTTPNotFound('No such page')
def check(match):
word = match.group(1)
exists = DBSession.query(Page).filter_by(name=word).all()
if exists:
view_url = request.route_url('view_page', pagename=word)
return '<a href="%s">%s</a>' % (view_url, word)
else:
add_url = request.route_url('add_page', pagename=word)
return '<a href="%s">%s</a>' % (add_url, word)
content = publish_parts(page.data, writer_name='html')['html_body']
content = wikiwords.sub(check, content)
edit_url = request.route_url('edit_page', pagename=pagename)
return dict(page=page, content=content, edit_url=edit_url)
|
The curried check()
function 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 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 response
object) is a cue to Pyramid that it should try to use a renderer
associated with the view configuration to render a template. In our case,
the template which will be rendered will be the templates/view.pt
template, as indicated in the @view_config
decorator that is applied to
view_page()
.
The add_page
view function¶
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.
1 2 3 4 5 6 7 8 9 10 11 12 | @view_config(route_name='add_page', renderer='templates/edit.pt')
def add_page(request):
name = request.matchdict['pagename']
if 'form.submitted' in request.params:
body = request.params['body']
page = Page(name, body)
DBSession.add(page)
return HTTPFound(location = request.route_url('view_page',
pagename=name))
save_url = request.route_url('add_page', pagename=name)
page = Page('', '')
return dict(page=page, save_url=save_url)
|
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 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.pt
) 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
. Pyramid will render the template associated
with this view to a response.
If the view execution is a result of a form submission (i.e. the expression
'form.submitted' in request.params
is True
), we scrape 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
DBSession.add
. We then redirect back to the view_page
view for the
newly created page.
The edit_page
view function¶
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.
1 2 3 4 5 6 7 8 9 10 11 12 13 | @view_config(route_name='edit_page', renderer='templates/edit.pt')
def edit_page(request):
name = request.matchdict['pagename']
page = DBSession.query(Page).filter_by(name=name).one()
if 'form.submitted' in request.params:
page.data = request.params['body']
DBSession.add(page)
return HTTPFound(location = request.route_url('view_page',
pagename=name))
return dict(
page=page,
save_url = request.route_url('edit_page', pagename=name),
)
|
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.
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.
Adding Templates¶
The views we’ve added all reference a template. Each template is a
Chameleon ZPT template. These templates will live in the
templates
directory of our tutorial package.
The view.pt
Template¶
The view.pt
template is used for viewing a single wiki page. It
is used by the view_page
view function. It should have a div
that is “structure replaced” with the content
value provided by
the view. It should also have a link on the rendered page that points
at the “edit” URL (the URL which invokes the edit_page
view for
the page being viewed).
Once we’re done with the view.pt
template, it will look a lot like the
below:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en"
xmlns:tal="http://xml.zope.org/namespaces/tal">
<head>
<title>${page.name} - Pyramid tutorial wiki (based on
TurboGears 20-Minute Wiki)</title>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8"/>
<meta name="keywords" content="python web application" />
<meta name="description" content="pyramid web application" />
<link rel="shortcut icon"
href="${request.static_url('tutorial:static/favicon.ico')}" />
<link rel="stylesheet"
href="${request.static_url('tutorial:static/pylons.css')}"
type="text/css" media="screen" charset="utf-8" />
<!--[if lte IE 6]>
<link rel="stylesheet"
href="${request.static_url('tutorial:static/ie6.css')}"
type="text/css" media="screen" charset="utf-8" />
<![endif]-->
</head>
<body>
<div id="wrap">
<div id="top-small">
<div class="top-small align-center">
<div>
<img width="220" height="50" alt="pyramid"
src="${request.static_url('tutorial:static/pyramid-small.png')}" />
</div>
</div>
</div>
<div id="middle">
<div class="middle align-right">
<div id="left" class="app-welcome align-left">
Viewing <b><span tal:replace="page.name">Page Name
Goes Here</span></b><br/>
You can return to the
<a href="${request.application_url}">FrontPage</a>.<br/>
</div>
<div id="right" class="app-welcome align-right"></div>
</div>
</div>
<div id="bottom">
<div class="bottom">
<div tal:replace="structure content">
Page text goes here.
</div>
<p>
<a tal:attributes="href edit_url" href="">
Edit this page
</a>
</p>
</div>
</div>
</div>
<div id="footer">
<div class="footer"
>© Copyright 2008-2011, Agendaless Consulting.</div>
</div>
</body>
</html>
Note
The names available for our use in a template are always
those that are present in the dictionary returned by the view
callable. But our templates make use of a request
object that
none of our tutorial views return in their dictionary. This value
appears as if “by magic”. However, request
is one of several
names that are available “by default” in a template when a template
renderer is used. See *.pt or *.txt: Chameleon Template Renderers for more
information about other names that are available by default in a
template when a Chameleon template is used as a renderer.
The edit.pt
Template¶
The edit.pt
template is used for adding and editing a wiki page. It is
used by the add_page
and edit_page
view functions. It should display
a page containing a form that POSTs back to the “save_url” argument supplied
by the view. The form should have a “body” textarea field (the page data),
and a submit button that has the name “form.submitted”. The textarea in the
form should be filled with any existing page data when it is rendered.
Once we’re done with the edit.pt
template, it will look a lot like
the following:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en"
xmlns:tal="http://xml.zope.org/namespaces/tal">
<head>
<title>${page.name} - Pyramid tutorial wiki (based on
TurboGears 20-Minute Wiki)</title>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8"/>
<meta name="keywords" content="python web application" />
<meta name="description" content="pyramid web application" />
<link rel="shortcut icon"
href="${request.static_url('tutorial:static/favicon.ico')}" />
<link rel="stylesheet"
href="${request.static_url('tutorial:static/pylons.css')}"
type="text/css" media="screen" charset="utf-8" />
<!--[if lte IE 6]>
<link rel="stylesheet"
href="${request.static_url('tutorial:static/ie6.css')}"
type="text/css" media="screen" charset="utf-8" />
<![endif]-->
</head>
<body>
<div id="wrap">
<div id="top-small">
<div class="top-small align-center">
<div>
<img width="220" height="50" alt="pyramid"
src="${request.static_url('tutorial:static/pyramid-small.png')}" />
</div>
</div>
</div>
<div id="middle">
<div class="middle align-right">
<div id="left" class="app-welcome align-left">
Editing <b><span tal:replace="page.name">Page Name Goes
Here</span></b><br/>
You can return to the
<a href="${request.application_url}">FrontPage</a>.<br/>
</div>
<div id="right" class="app-welcome align-right"></div>
</div>
</div>
<div id="bottom">
<div class="bottom">
<form action="${save_url}" method="post">
<textarea name="body" tal:content="page.data" rows="10"
cols="60"/><br/>
<input type="submit" name="form.submitted" value="Save"/>
</form>
</div>
</div>
</div>
<div id="footer">
<div class="footer"
>© Copyright 2008-2011, Agendaless Consulting.</div>
</div>
</body>
</html>
Static Assets¶
Our templates name a single static asset named pylons.css
. We don’t need
to create this file within our package’s static
directory because it was
provided at the time we created the project. This file is a little too long
to replicate within the body of this guide, however it is available online.
This CSS file will be accessed via
e.g. http://localhost:6543/static/pylons.css
by virtue of the call to
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
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 namedview_wiki
. It maps to ourview_wiki
view callable by virtue of the@view_config
attached to theview_wiki
view function indicatingroute_name='view_wiki'
. - Add a declaration which maps the pattern
/{pagename}
to the route namedview_page
. This is the regular view for a page. It maps to ourview_page
view callable by virtue of the@view_config
attached to theview_page
view function indicatingroute_name='view_page'
. - Add a declaration which maps the pattern
/add_page/{pagename}
to the route namedadd_page
. This is the add view for a new page. It maps to ouradd_page
view callable by virtue of the@view_config
attached to theadd_page
view function indicatingroute_name='add_page'
. - Add a declaration which maps the pattern
/{pagename}/edit_page
to the route namededit_page
. This is the edit view for a page. It maps to ouredit_page
view callable by virtue of the@view_config
attached to theedit_page
view function indicatingroute_name='edit_page'
.
As a result of our edits, the __init__.py
file should look
something like:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | from pyramid.config import Configurator
from sqlalchemy import engine_from_config
from .models import DBSession
def main(global_config, **settings):
""" This function returns a Pyramid WSGI application.
"""
engine = engine_from_config(settings, 'sqlalchemy.')
DBSession.configure(bind=engine)
config = Configurator(settings=settings)
config.add_static_view('static', 'static', cache_max_age=3600)
config.add_route('view_wiki', '/')
config.add_route('view_page', '/{pagename}')
config.add_route('add_page', '/add_page/{pagename}')
config.add_route('edit_page', '/{pagename}/edit_page')
config.scan()
return config.make_wsgi_app()
|
(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 Starting the Application). The views we’ll try are as follows:
- Visiting
http://localhost:6543
in a browser invokes theview_wiki
view. This always redirects to theview_page
view of the FrontPage page object. - Visiting
http://localhost:6543/FrontPage
in a browser invokes theview_page
view of the front page page object. - Visiting
http://localhost:6543/FrontPage/edit_page
in a browser invokes the edit view for the front page object. - Visiting
http://localhost:6543/add_page/SomePageName
in a browser invokes the add view for a page.
Try generating an error within the body of a view by adding code to
the top of it that generates an exception (e.g. raise
Exception('Forced Exception')
). Then visit the error-raising view
in a browser. You should see an interactive exception handler in the
browser which allows you to examine values in a post-mortem mode.