repoze.bfg Introduction¶
repoze.bfg is a Python web framework. It is inspired by Zope, Pylons, and Django. repoze.bfg uses the WSGI protocol to handle requests and responses.
Similarities to Other Frameworks¶
repoze.bfg was inspired by Zope, Pylons and Django.
The repoze.bfg concept of traversal is inspired by Zope. Additionally, repoze.bfg uses the Zope Component Architecture internally, as do Zope 2, Zope 3, and Grok. repoze.bfg application developers may use either ZCML (an XML dialect, used in Zope) or decorators to perform various application configuration tasks. The decorator support is provided by the Grok project. Like Zope, repoze.bfg allows you to create applications which do not need to be forked or otherwise modified to be extended by a third party developer.
The repoze.bfg concept of URL dispatch is inspired by Pylons. Like Pylons, repoze.bfg is mostly policy-free. It makes no assertions about which database you should use, and its built-in templating facilities are only for convenience. In essence, it only supplies a mechanism to map URLs to view code, along with a convention for calling those views. You are free to use third-party components in your application that fit your needs. Also like Pylons, repoze.bfg is dependent upon WSGI.
The Django docs state that Django is not an “MVC” (model/view/controller) framework in their FAQ. repoze.bfg isn’t either. Django’s documentation does a good job of why explaining why they don’t use “MVC” acronym:
Django appears to be a MVC framework, but you call the Controller the “view”, and the View the “template”. How come you don’t use the standard names?
Well, the standard names are debatable.
In our interpretation of MVC, the “view” describes the data that gets presented to the user. It’s not necessarily how the data looks, but which data is presented. The view describes which data you see, not how you see it. It’s a subtle distinction.
So, in our case, a “view” is the Python callback function for a particular URL, because that callback function describes which data is presented.
Furthermore, it’s sensible to separate content from presentation - which is where templates come in. In Django, a “view” describes which data is presented, but a view normally delegates to a template, which describes how the data is presented.
Where does the “controller” fit in, then? In Django’s case, it’s probably the framework itself: the machinery that sends a request to the appropriate view, according to the Django URL configuration.
repoze.bfg uses terminology similar to Django. The skeleton code generator of repoze.bfg generates a directory layout very similar to the directory layout suggested by the Django Book . Additionally, as suggested above, the concepts of view, model and template are used by repoze.bfg as they would be by Django.
Differences from Other Frameworks¶
Like Zope, the repoze.bfg framework imposes more control inversion upon application developers than other Python frameworks such as Pylons. For example repoze.bfg allows you to explicitly resolve a URL to a context object before invoking a view. Pylons and other Python “MVC” frameworks have no such intermediate step; they resolve a URL directly to a controller. Another example: using the repoze.bfg security subsystem assumes that you’re willing to attach an ACL to a context object; the ACL is checked by the framework itself instead of by user code, and access is permitted or denied by the framework itself rather than by user code. Such a task would typically be performed by user-space decorators in other Python web frameworks.
Like Zope, but unlike Pylons applications or most Django applications, when you build a repoze.bfg application, if you obey certain constraints, the application you produce can be reused, modified, re-integrated, or extended by third-party developers without modification to the original application itself. See Extending An Existing repoze.bfg Application for more information about extending or modifying an existing repoze.bfg application.
repoze.bfg uses the Zope Component Architecture under the hood. However, while a Zope application developer tends to need to understand the component architecture (and concepts such as adapters, utilities, and interfaces) to create a non-trivial application, a repoze.bfg application developer isn’t required to interact with or understand the component architecture at all. repoze.bfg tends to “hide” most interaction with the component architecture behind special-purpose API functions and ZCML directives.
Also unlike Zope and unlike other “full-featured” frameworks such as Django, repoze.bfg makes no assumptions about which persistence mechanisms you should use to build an application. Zope applications are typically reliant on ZODB; repoze.bfg allows you to build ZODB applications, but it has no reliance on the ZODB package. Likewise, Django tends to assume that you want to store your application’s data in a relational database. repoze.bfg makes no such assumption; it allows you to use a relational database but doesn’t encourage or discourage an application developer about such a decision.
Why?¶
Familiarity: As web developers, we’ve become accustomed to working in very particular ways over the years. This framework is a canonization of practices that “fit our brains”.
Simplicity: repoze.bfg attempts to be a “pay only for what you eat” framework in which you can be productive quickly with partial knowledge. We contrast this with “pay up front for what anyone might eventually want to eat” frameworks, which tend to expect you to understand a great many concepts and technologies fully before you can be truly productive. repoze.bfg doesn’t force you to use any particular technology to produce an application, and we try to keep the core set of concepts you need to understand to a minimum.
Minimalism: repoze.bfg provides only the very basics: URL to code mapping, templating, security, and resources. There is not much more to the framework than these pieces: you are expected to provide the rest.
Documentation: Because repoze.bfg is minimal, it’s relatively easy to keep its documentation up-to-date, which is helpful to bring new developers up to speed. It’s our goal that nothing remain undocumented about repoze.bfg.
Speed: repoze.bfg is faster than many other popular Python web frameworks for common tasks such as templating and simple response generation. The “hardware is cheap” mantra has its limits when you’re responsible for managing a great many machines: the fewer you need, the less pain you’ll have.
It’s Tested¶
If it ain’t tested, it’s broke. We strive to test repoze.bfg completely. Below a run of the nosetests command configured to show code coverage information (run against the repoze.bfg trunk as of the 1.0 release).
[chrism@vitaminf trunk]$ python setup.py nosetests
running nosetests
running egg_info
writing requirements to repoze.bfg.egg-info/requires.txt
writing repoze.bfg.egg-info/PKG-INFO
writing namespace_packages to repoze.bfg.egg-info/namespace_packages.txt
writing top-level names to repoze.bfg.egg-info/top_level.txt
writing dependency_links to repoze.bfg.egg-info/dependency_links.txt
writing entry points to repoze.bfg.egg-info/entry_points.txt
writing manifest file 'repoze.bfg.egg-info/SOURCES.txt'
running build_ext
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Name Stmts Exec Cover Missing
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repoze.bfg 0 0 100%
repoze.bfg.authentication 196 196 100%
repoze.bfg.authorization 50 50 100%
repoze.bfg.chameleon_text 48 48 100%
repoze.bfg.chameleon_zpt 41 41 100%
repoze.bfg.events 18 18 100%
repoze.bfg.functional 14 14 100%
repoze.bfg.includes 0 0 100%
repoze.bfg.interfaces 73 73 100%
repoze.bfg.location 10 10 100%
repoze.bfg.log 9 9 100%
repoze.bfg.paster 48 48 100%
repoze.bfg.path 28 28 100%
repoze.bfg.registry 51 51 100%
repoze.bfg.request 67 67 100%
repoze.bfg.resource 83 83 100%
repoze.bfg.router 167 167 100%
repoze.bfg.scripting 10 10 100%
repoze.bfg.secpols 166 166 100%
repoze.bfg.security 114 114 100%
repoze.bfg.settings 35 35 100%
repoze.bfg.static 48 48 100%
repoze.bfg.templating 35 35 100%
repoze.bfg.testing 218 218 100%
repoze.bfg.tests 0 0 100%
repoze.bfg.tests.fixtureapp 0 0 100%
repoze.bfg.tests.fixtureapp.models 4 4 100%
repoze.bfg.tests.fixtureapp.subpackage 0 0 100%
repoze.bfg.tests.fixtureapp.views 4 4 100%
repoze.bfg.tests.grokkedapp 9 9 100%
repoze.bfg.tests.routesapp 0 0 100%
repoze.bfg.tests.routesapp.views 4 4 100%
repoze.bfg.tests.test_authentication 433 433 100%
repoze.bfg.tests.test_authorization 124 124 100%
repoze.bfg.tests.test_chameleon_text 172 172 100%
repoze.bfg.tests.test_chameleon_zpt 161 161 100%
repoze.bfg.tests.test_events 59 59 100%
repoze.bfg.tests.test_integration 123 123 100%
repoze.bfg.tests.test_location 34 34 100%
repoze.bfg.tests.test_log 11 11 100%
repoze.bfg.tests.test_paster 69 69 100%
repoze.bfg.tests.test_path 104 104 100%
repoze.bfg.tests.test_registry 95 95 100%
repoze.bfg.tests.test_request 230 230 100%
repoze.bfg.tests.test_resource 233 233 100%
repoze.bfg.tests.test_router 830 830 100%
repoze.bfg.tests.test_scripting 44 44 100%
repoze.bfg.tests.test_secpols 598 598 100%
repoze.bfg.tests.test_security 294 294 100%
repoze.bfg.tests.test_settings 137 137 100%
repoze.bfg.tests.test_static 120 120 100%
repoze.bfg.tests.test_templating 126 126 100%
repoze.bfg.tests.test_testing 394 394 100%
repoze.bfg.tests.test_threadlocal 69 69 100%
repoze.bfg.tests.test_traversal 906 906 100%
repoze.bfg.tests.test_url 173 173 100%
repoze.bfg.tests.test_urldispatch 166 166 100%
repoze.bfg.tests.test_view 409 409 100%
repoze.bfg.tests.test_wsgi 99 99 100%
repoze.bfg.tests.test_zcml 1290 1290 100%
repoze.bfg.threadlocal 29 29 100%
repoze.bfg.traversal 200 200 100%
repoze.bfg.url 63 63 100%
repoze.bfg.urldispatch 101 101 100%
repoze.bfg.view 72 72 100%
repoze.bfg.wsgi 27 27 100%
repoze.bfg.zcml 274 274 100%
----------------------------------------------------------------------
TOTAL 9819 9819 100%
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Ran 644 tests in 22.150s
OK
