The repoze.bfg framework allows Zope developers to use WSGI technologies more easily and non-Zope developers to use Zope technologies without all of Zope. It provides URL dispatch, templating, and declarative security while avoiding features like databases, sessions, and the ZMI. Repoze.bfg uses the Zope Component Architecture and aims for familiarity, simplicity, speed, documentation, and collaboration.

1. the
repoze.bfg
web framework
Presented By
Chris McDonough
Agendaless Consulting
Plone Conference 2008

2. • About a year old.
• Allow Zope developers to use WSGI
technologies more easily.
• Allow non-Zope developers to use Zope
technologies without using all of Zope.

3. • repoze.bfg: July 2008
• Chris McDonough, Tres Seaver, Paul Everitt,
Carlos de la Guardia, Malthe Borch, Stefan
Eletzhofer, Fernando Neto-Correa.
• Big f'ing gun -OR- big friendly giant: you
choose.

5. WHY?
• Zope2: still kicking, but only due to Plone
• Zope3: big, many dependencies. App developers
encouraged to use CA.
• Grok: quot;making Z3 easier to usequot; (see Zope 3).
• Django: nice, but Z2-like.
• Pylons/TG2: nice, but geared towards RDB / URL
dispatch apps.
• Others: not Zope-like / no traction.

6. Goals
• Familiarity: like Zope, but less
• Simplicity: pay only for what you eat
• Speed: go as fast as possible while still actually
doing something
• Documentation: the lack of formal
documentation of a feature or API is a bug
• Collaboration: culture of using and promoting
non-Zope stuff

7. What BFG Does
• Maps URLs to code
• Provides mechanisms that allow developers
to make declarative security assertions
• Provides text and HTML templating
facilities
• Allows for use of existing Zope libs (via
ZCML).

8. What BFG Doesn't Do
• Database / persistence
• Sessions
• Indexing / searching
• ZMI / TTW code
• View code sharing with Z3 / Five
• etc...

9. The Application is the
Application
• You don't write quot;Productsquot; to plug into
BFG. Extensibility is via normal Python
packages and ZCML as necessary.
• An application is generated for you; you
develop the application and run the
application; you don't run the framework.

10. Graph Traversal and
URL Dispatch
• BFG supports both graph traversal (ala
Zope) and quot;URL dispatchquot; (ala everything
else) to map URLs to code.
• URL dispatch is backed by Routes.

11. Zope CA
• The Zope Component Architecture was
used to construct BFG.
• BFG application developers don't
need to use the CA. It's a framework
implementation detail.

12. Components
• WSGI pipeline.
• Router (aka Publisher).
• quot;Application registryquot; (ZCML / decorators).
• Views (aka quot;controllersquot; in Pylons/Rails).
• Templates (chameleon/XSL/other).

13. Dependencies
Paste-1.7.1-py2.4.egg zope.deferredimport-3.4.0-py2.4.egg
PasteDeploy-1.3.2-py2.4.egg zope.deprecation-3.4.0-py2.4.egg
PasteScript-1.6.3-py2.4.egg zope.event-3.4.0-py2.4.egg
Routes-1.9.2-py2.4.egg zope.exceptions-3.5.2-py2.4.egg
WebOb-0.9.2-py2.4.egg zope.hookable-3.4.0-py2.4-macosx-10.5-i386.egg
zope.i18n-3.5.0-py2.4.egg zope.proxy-3.4.1-py2.4-macosx-10.5-i386.egg
elementtree-1.2.6_20050316-py2.4.egg zope.i18nmessageid-3.4.3-py2.4-macosx-10.5-i386.egg
lxml-2.1.1-py2.4-macosx-10.5-i386.egg zope.interface-3.4.1-py2.4-macosx-10.5-i386.egg
pytz-2008c-py2.4.egg zope.location-3.4.0-py2.4.egg
setuptools-0.6c8-py2.4.egg zope.publisher-3.5.3-py2.4.egg
zope.schema-3.4.0-py2.4.egg zope.traversing-3.5.0a3-py2.4.egg
z3c.pt-1.0a1-py2.4.egg zope.security-3.5.1-py2.4-macosx-10.5-i386.egg
zope.component-3.4.0-py2.4.egg zope.testing-3.5.1-py2.4.egg
zope.configuration-3.4.0-py2.4.egg
Many are due to inappropriate dependencies in Zope
eggs.

14. How it Works

15. Models
• quot;contentquot; objects
• typically arranged
in a graph (although
not required)
• For Zope people: think ZODB
• ZODB not required for repoze.bfg
applications: filesystem directories, XML
documents, RDF graphs, SQL databases,
etc. can be the source of model data

16. A Model
from zope.interface import implements
from zope.interface import Interface
class IMyModel(Interface):
pass
class MyModel(object):
implements(IMyModel)
def __init__(self, name):
self.name = name

17. Views
• Views are functions which accept a
quot;contextquot; (a model object) and a quot;requestquot;.
• Views must return a response. Unlike Zope.
• The view may use a template to generate
the response body, or not.

18. A View
from webob import Response
def hello_world(context, request):
return Response('Hello world!')

19. A View That Renders a
chameleon.zpt Template
from repoze.bfg.chameleon_zpt
import render_template_to_response
def hello_world(context, request):
render_template_to_response(
'templates/hello.pt',
context=context,
myname='chris')

20. Using Model Data from
a View
from webob import Response
def hello_world(context, request):
name = context.name
return Response('Hello %s!' %
name)

21. Templates
• Default templating engine: chalmeleon by
Malthe Borch. ZPT or Genshi syntax. ~
10X - 15X faster than zope.pagetemplate.
• Included: XSLT.
• Add-on: jinja2 (Django-style, via
repoze.bfg.jinja2)
• Any other you'd like to use; bindings are
simple to create (see the jinja2 bindings).

22. Traversal
• The BFG router traverses the model graph based on
the path segments in the URL (like Zope does).
• If traversal quot;falls offquot; the end of the model graph,
and there are path segments remaining, it looks for
a view registered against the interface of the last
model traversed using the next path segment as
the view name.
• If there are no segments remaining, the default view
is used.
• If no view is found, a 404 not found error is
returned.

23. View Registrations
<configure xmlns=quot;http://namespaces.zope.org/zopequot;
xmlns:bfg=quot;http://namespaces.repoze.org/bfgquot;
i18n_domain=quot;repoze.bfgquot;>
<include package=quot;repoze.bfgquot; />
<— default view for .interfaces.IMyModel —>
<bfg:view
for=quot;.interfaces.IMyModelquot;
view=quot;.views.my_viewquot;
/>
<— named view for .interfaces.IMyModel —>
<bfg:view
for=quot;.interfaces.IMyModelquot;
view=quot;.views.other_viewquot;
name=quot;otherquot;
/>
</configure>

24. View Registrations via
Decorators
from webob import Response
from repoze.bfg.convention import
bfg_view
@bfg_view(name='hello.html')
def hello_world(context, request):
name = context.name
return Response('Hello %s!' %
name)

25. Speed
<html xmlns=quot;http://www.w3.org/1999/xhtmlquot;
xmlns:tal=quot;http://xml.zope.org/namespaces/talquot;>
<head>
<title tal:content=quot;context.titlequot;>The title</title>
<meta http-equiv=quot;content-typequot; content=quot;text/html;charset=utf-8quot;/>
</head>
<body>
<h2><span tal:replace=quot;context.title_or_id()quot;>content title or id</span>
<span tal:condition=quot;context.titlequot;
tal:replace=quot;context.titlequot;>optional template title</span></h2>
This is Page Template <em tal:content=quot;request.view_namequot;>template id</em>.
</body>
</html>
Zope 2.10 view page template: 309 req/sec
vs.
BFG view + chameleon.zpt template: 869 req/sec

26. Memory Usage and
Process Sharing
• Existing Zope 2 and Zope 3 apps cannot
run side-by-side in the same process due to
globals sharing (ZCML global registry,
database references); BFG has been written
to make such a configuration work by
default.
• Lower memory requirements per
application instance (BFG minimum ~15 MB
vs. Zope 3 minimum ~50MB).

27. Startup Speed
• repoze.bfg caches the ZCML registry as a
pickle for faster startup.
• Startup time with a single view defined:
900ms.

28. Paste-Derived Reload
Feature
[chrism@vitaminf myproj]$ ../bin/paster serve myproj.ini —reload
Starting subprocess with file monitor
Starting server in PID 61405.
serving on 0.0.0.0:6543 view at http://127.0.0.1:6543
/Users/chrism/projects/repoze/bfgenv/myproj/myproj/run.py
changed; reloading...
—————————— Restarting ——————————
Starting server in PID 61409.
serving on 0.0.0.0:6543 view at http://127.0.0.1:6543

29. Template Auto-Reload
Feature
• Templates auto-reload by default.
• This can be turned off for speed.

30. WSGI-Middleware-
Derived Features
• Profiler (repoze.profile)
• Alternate exception handlers
(paste.evalexception).
• Caching (repoze.accelerator)
• Theming (Deliverance).
• Transaction management (repoze.tm2)
• etc...

31. Project Setup Demo

32. Futures
• Vudo CMS (http://docs.vudo.me) to be
implemented using repoze.bfg, hopefully.
Work towards this: repoze.bfg.skins,
repoze.bfg.layout, repoze.bitblt,
repoze.squeeze.
• BFG will stay minimal. Add-ons and
superframeworks like vudo and
repoze.lemonade will provide functionality.

33. The End
• For a more in-depth exploration of how a
bfg app is written, see the screencast at
http://static.repoze.org/presentations/repozebfg-wiki.mov