Defining Views¶
A view callable in a url dispatch -based 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.
Note
A Pyramid view can also be defined as callable which accepts two
arguments: a context and a request. You’ll see this
two-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 url
dispatch based applications, however, the context object is rarely used in
the view body itself, so within this tutorial we define views as callables
that accept only a request to avoid the visual “noise”. 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
.
The request 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/1.0-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 paster create
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
install_requires
parameter in the setup
function.
Our resulting setup.py
should look like so:
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 | import os
import sys
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',
'repoze.tm2>=1.0b1', # default_commit_veto
'zope.sqlalchemy',
'WebError',
'docutils',
]
if sys.version_info[:3] < (2,5,0):
requires.append('pysqlite')
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
""",
paster_plugins=['pyramid'],
)
|
Note
After these new dependencies are 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 package.
Adding View Functions¶
We’ll get rid of our my_view
view function in our views.py
file. It’s only an example and isn’t relevant to our application.
Then we’re going to add four view callable functions to our
views.py
module. One view callable (named view_wiki
) will
display the wiki itself (it will answer on the root URL), another
named view_page
will display an individual page, another named
add_page
will allow a page to be added, and a final view callable
named edit_page
will allow a page to be edited. 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¶
The view_wiki
function will respond as the default view of
a Wiki
model object. It always redirects to a URL which
represents the path to our “FrontPage”. It returns an instance of the
pyramid.httpexceptions.HTTPFound
class (instances of which
implement the WebOb response interface), It will use the
pyramid.url.route_url()
API to construct a URL to the
FrontPage
page (e.g. http://localhost:6543/FrontPage
), and
will use it as the “location” of the HTTPFound response, forming an
HTTP redirect.
The view_page
view function¶
The view_page
function will respond as the default view of
a Page
object. The view_page
function 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.
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, 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 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 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 this view 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 per the
configuration put into effect in __init__.py
.
The add_page
view function¶
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 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 pagename
value in the matchdict will be SomeName
.
If the view execution is not a result of a form submission (if 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 use 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, so we create a dummy Page object in order to satisfy the edit
form’s desire to have some page object exposed as page
, and
Pyramid will render the template associated with this view
to a response.
If the view execution is a result of a form submission (if the
expression 'form.submitted' in request.params
is True
), we
scrape the page body from the form data, create a Page object using
the name in the matchdict pagename
, and obtain the page body from
the request, and save it into the database using session.add
. 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¶
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 handler for the form it renders. The
matchdict
attribute of the request passed to the add_page
view
will have a pagename
key matching the name of the page the user
wants to edit.
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 request, 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 (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
key in the matchdict. It then redirects to the
default view of the wiki page, which will always be the view_page
view.
Viewing the Result of Our Edits to views.py
¶
The result of all of our edits to views.py
will leave it looking
like this:
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 | import re
from docutils.core import publish_parts
from pyramid.httpexceptions import HTTPFound
from pyramid.url import route_url
from tutorial.models import DBSession
from tutorial.models import Page
# regular expression used to find WikiWords
wikiwords = re.compile(r"\b([A-Z]\w+[A-Z]+\w+)")
def view_wiki(request):
return HTTPFound(location = route_url('view_page', request,
pagename='FrontPage'))
def view_page(request):
matchdict = request.matchdict
session = DBSession()
page = session.query(Page).filter_by(name=matchdict['pagename']).one()
def check(match):
word = match.group(1)
exists = session.query(Page).filter_by(name=word).all()
if exists:
view_url = route_url('view_page', request, pagename=word)
return '<a href="%s">%s</a>' % (view_url, word)
else:
add_url = route_url('add_page', request, 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 = route_url('edit_page', request,
pagename=matchdict['pagename'])
return dict(page=page, content=content, edit_url=edit_url)
def add_page(request):
name = request.matchdict['pagename']
if 'form.submitted' in request.params:
session = DBSession()
body = request.params['body']
page = Page(name, body)
session.add(page)
return HTTPFound(location = route_url('view_page', request,
pagename=name))
save_url = route_url('add_page', request, pagename=name)
page = Page('', '')
return dict(page=page, save_url=save_url)
def edit_page(request):
name = request.matchdict['pagename']
session = DBSession()
page = session.query(Page).filter_by(name=name).one()
if 'form.submitted' in request.params:
page.data = request.params['body']
session.add(page)
return HTTPFound(location = route_url('view_page', request,
pagename=name))
return dict(
page=page,
save_url = route_url('edit_page', request, pagename=name),
)
|
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 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="${request.static_url('tutorial:static/pyramid-small.png')}" />
</div>
</div>
</div>
<div id="middle">
<div class="middle align-right">
<div id="left" class="app-welcome align-left">
Editing <b><span tal:replace="page.name">Page Name Goes
Here</span></b><br/>
You can return to the
<a href="${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__
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.
Mapping Views to URLs in __init__.py
¶
The __init__.py
file contains
pyramid.config.Configurator.add_route()
calls which serve to map
URLs via url dispatch to view functions. 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 view namedview_wiki
in ourviews.py
file with the nameview_wiki
. This is the default view for the wiki. - Add a declaration which maps the pattern
/{pagename}
to the view namedview_page
in ourviews.py
file with the view nameview_page
. This is the regular view for a page. - Add a declaration which maps the pattern
/add_page/{pagename}
to the view namedadd_page
in ourviews.py
file with the nameadd_page
. This is the add view for a new page. - Add a declaration which maps the pattern
/{pagename}/edit_page
to the view namededit_page
in ourviews.py
file with the nameedit_page
. This is the edit view for a page.
As a result of our edits, the __init__.py
file should look
something like so:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | from pyramid.config import Configurator
from sqlalchemy import engine_from_config
from tutorial.models import initialize_sql
def main(global_config, **settings):
""" This function returns a WSGI application.
"""
engine = engine_from_config(settings, 'sqlalchemy.')
initialize_sql(engine)
config = Configurator(settings=settings)
config.add_static_view('static', 'tutorial:static')
config.add_route('view_wiki', '/', view='tutorial.views.view_wiki')
config.add_route('view_page', '/{pagename}',
view='tutorial.views.view_page',
view_renderer='tutorial:templates/view.pt')
config.add_route('add_page', '/add_page/{pagename}',
view='tutorial.views.add_page',
view_renderer='tutorial:templates/edit.pt')
config.add_route('edit_page', '/{pagename}/edit_page',
view='tutorial.views.edit_page',
view_renderer='tutorial:templates/edit.pt')
return config.make_wsgi_app()
|
Viewing the Application in a Browser¶
We can finally examine our application in a browser. 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.
Adding Tests¶
Since we’ve added a good bit of imperative code here, it’s useful to define tests for the views we’ve created. We’ll change our tests.py module to look like this:
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 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 | import unittest
from pyramid import testing
def _initTestingDB():
from tutorial.models import DBSession
from tutorial.models import Base
from sqlalchemy import create_engine
engine = create_engine('sqlite://')
DBSession.configure(bind=engine)
Base.metadata.bind = engine
Base.metadata.create_all(engine)
return DBSession
def _registerRoutes(config):
config.add_route('view_page', '{pagename}')
config.add_route('edit_page', '{pagename}/edit_page')
config.add_route('add_page', 'add_page/{pagename}')
class ViewWikiTests(unittest.TestCase):
def setUp(self):
self.config = testing.setUp()
def tearDown(self):
testing.tearDown()
def test_it(self):
from tutorial.views import view_wiki
self.config.add_route('view_page', '{pagename}')
request = testing.DummyRequest()
response = view_wiki(request)
self.assertEqual(response.location, 'http://example.com/FrontPage')
class ViewPageTests(unittest.TestCase):
def setUp(self):
self.session = _initTestingDB()
self.config = testing.setUp()
def tearDown(self):
self.session.remove()
testing.tearDown()
def _callFUT(self, request):
from tutorial.views import view_page
return view_page(request)
def test_it(self):
from tutorial.models import Page
request = testing.DummyRequest()
request.matchdict['pagename'] = 'IDoExist'
page = Page('IDoExist', 'Hello CruelWorld IDoExist')
self.session.add(page)
_registerRoutes(self.config)
info = self._callFUT(request)
self.assertEqual(info['page'], page)
self.assertEqual(
info['content'],
'<div class="document">\n'
'<p>Hello <a href="http://example.com/add_page/CruelWorld">'
'CruelWorld</a> '
'<a href="http://example.com/IDoExist">'
'IDoExist</a>'
'</p>\n</div>\n')
self.assertEqual(info['edit_url'],
'http://example.com/IDoExist/edit_page')
class AddPageTests(unittest.TestCase):
def setUp(self):
self.session = _initTestingDB()
self.config = testing.setUp()
self.config.begin()
def tearDown(self):
self.session.remove()
testing.tearDown()
def _callFUT(self, request):
from tutorial.views import add_page
return add_page(request)
def test_it_notsubmitted(self):
_registerRoutes(self.config)
request = testing.DummyRequest()
request.matchdict = {'pagename':'AnotherPage'}
info = self._callFUT(request)
self.assertEqual(info['page'].data,'')
self.assertEqual(info['save_url'],
'http://example.com/add_page/AnotherPage')
def test_it_submitted(self):
from tutorial.models import Page
_registerRoutes(self.config)
request = testing.DummyRequest({'form.submitted':True,
'body':'Hello yo!'})
request.matchdict = {'pagename':'AnotherPage'}
self._callFUT(request)
page = self.session.query(Page).filter_by(name='AnotherPage').one()
self.assertEqual(page.data, 'Hello yo!')
class EditPageTests(unittest.TestCase):
def setUp(self):
self.session = _initTestingDB()
self.config = testing.setUp()
def tearDown(self):
self.session.remove()
testing.tearDown()
def _callFUT(self, request):
from tutorial.views import edit_page
return edit_page(request)
def test_it_notsubmitted(self):
from tutorial.models import Page
_registerRoutes(self.config)
request = testing.DummyRequest()
request.matchdict = {'pagename':'abc'}
page = Page('abc', 'hello')
self.session.add(page)
info = self._callFUT(request)
self.assertEqual(info['page'], page)
self.assertEqual(info['save_url'],
'http://example.com/abc/edit_page')
def test_it_submitted(self):
from tutorial.models import Page
_registerRoutes(self.config)
request = testing.DummyRequest({'form.submitted':True,
'body':'Hello yo!'})
request.matchdict = {'pagename':'abc'}
page = Page('abc', 'hello')
self.session.add(page)
response = self._callFUT(request)
self.assertEqual(response.location, 'http://example.com/abc')
self.assertEqual(page.data, 'Hello yo!')
|
We can then run the tests using something like:
1 | $ python setup.py test -q
|
The expected output is something like:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | running test
running egg_info
writing requirements to tutorial.egg-info/requires.txt
writing tutorial.egg-info/PKG-INFO
writing top-level names to tutorial.egg-info/top_level.txt
writing dependency_links to tutorial.egg-info/dependency_links.txt
writing entry points to tutorial.egg-info/entry_points.txt
unrecognized .svn/entries format in
reading manifest file 'tutorial.egg-info/SOURCES.txt'
writing manifest file 'tutorial.egg-info/SOURCES.txt'
running build_ext
......
----------------------------------------------------------------------
Ran 6 tests in 0.181s
OK
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