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:mod:`repoze.bfg` Introduction
==============================
:mod:`repoze.bfg` is a Python web application framework. It is
inspired by Zope, and uses :term:`Zope` libraries to do much of its
work. However, it is simpler than any released version of Zope.
:mod:`repoze.bfg` uses the :term:`WSGI` protocol to handle requests
and responses.
Similarities to Other Frameworks
--------------------------------
:mod:`repoze.bfg` was inspired by :term:`Zope`, :term:`Django`, and
:term:`Pylons`.
The :mod:`repoze.bfg` concept of traversal is inspired by
:term:`Zope`. Additionally, :mod:`repoze.bfg` uses the Zope Component
Architecture ("CA") internally, as do Zope 2, Zope 3, and
:term:`Grok`. Application :mod:`repoze.bfg` developers use either
:term:`ZCML` (an XML dialect, used in Zope) or decorators to perform
various configuration tasks. The decorator support is provided by the
:term:`Grok` project.
Like :term:`Pylons`, :mod:`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 :term:`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, :mod:`repoze.bfg` is heavily dependent on WSGI.
The "Django docs state that Django is an "MTV" framework in their `FAQ
<http://www.djangoproject.com/documentation/faq/>`_. This also
happens to be true for :mod:`repoze.bfg`::
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.
If you're hungry for acronyms, you might say that Django is a "MTV"
framework - that is, "model", "template", and "view." That breakdown
makes much more sense.
The skeleton code generator of :mod:`repoze.bfg` generates a directory
layout very simliar to the directory layout suggested by the `Django
Book <http://www.djangobook.com/>`_ . Additionally, as suggested
above, the concepts of :term:`view`, :term:`model` and
:term:`template` are used by :mod:`repoze.bfg` as they would be by
Django.
To learn more about the concepts used by :mod:`repoze.bfg`, visit the
:ref:`glossary` for a listing of definitions.
Differences from Other Frameworks
---------------------------------
Like :term:`Zope`, the :mod:`repoze.bfg` framework imposes slightly
more `control inversion <http://plope.com/control_inversion>`_ upon
application developers than other Python frameworks such as
:term:`Pylons`. For example :mod:`repoze.bfg` assumes that you're
wiling to resolve a URL to a :term:`context` object before passing it
to a :term:`view`. Pylons and other Python "MVC" frameworks have no
such intermediate step; they resolve a URL directly to a controller.
Another example: using the :mod:`repoze.bfg` security subsystem
assumes that you're willing to attach an :term:`ACL` to a
:term:`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.
Unlike application development using Zope, application developers
don't interact with the Zope Component Architecture ("CA") very much
during :mod:`repoze.bfg` application development. Instead, the
:mod:`repoze.bfg` framework tends to "hide" most interaction with the
CA behind special-purpose API functions.
Also unlike :term:`Zope` and unlike other "full-featured" frameworks
such as :term:`Django`, :mod:`repoze.bfg` makes no assumptions about
what persistence mechanisms you want to use to build an application.
Zope applications are typically reliant on :term:`ZODB`;
:mod:`repoze.bfg` allows you to build :term:`ZODB` applications, but
it has no reliance on the ZODB package. Likewise, :term:`Django`
tends to make the assumption that you're going to want to store your
application's data in a relational database. :mod:`repoze.bfg` makes
no such assumption; it allows you to use a relational database but
doesn't enourage or discourage an application developer about such a
decision.
Why?
----
*Familiarity*: As web developers, we've become accustomed to working
in very particular ways (primarily using Zope 2) over the years. This
framework is a canonization of practices that "fit our brains".
*Simplicity*: :mod:`repoze.bfg` attempts to be a *"pay only for what
you eat"* framework in which you can be productive quickly with
partial knowledge, in contrast to *"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. :mod:`repoze.bfg` doesn't force you to use any
particular technology to get your application written, and we try to
keep the core set of concepts you need to understand to a minimum.
We've thrown out all the cruft.
*Minimalism*: :mod:`repoze.bfg` provides only the very basics: *URL to
code mapping*, *templating*, and *security*. There is not much more
to the framework than these pieces: you are expected to provide the
rest.
*Documentation*: Because :mod:`repoze.bfg` is so 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 :mod:`repoze.bfg`.
*Speed*: :mod:`repoze.bfg` is meant to be fast, capable of serving on
the order of 100-1000 requests per second on today's commodity
hardware for views that do "real work" given proper application
implementation. 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 :mod:`repoze.bfg`
completely. Below a run of the ``nosetests`` command configured to
show code coverage information (run against the :mod:`repoze.bfg`
trunk as of the 0.8a6 release).
.. code-block:: bash
[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
..........................................................................
..........................................................................
..........................................................................
..........................................................................
..........................................................................
....
Name Stmts Exec Cover Missing
--------------------------------------------------------------------
repoze.bfg 0 0 100%
repoze.bfg.chameleon_text 48 48 100%
repoze.bfg.chameleon_zpt 44 44 100%
repoze.bfg.events 18 18 100%
repoze.bfg.functional 14 14 100%
repoze.bfg.includes 0 0 100%
repoze.bfg.interfaces 71 71 100%
repoze.bfg.location 14 14 100%
repoze.bfg.log 9 9 100%
repoze.bfg.lru 75 75 100%
repoze.bfg.path 12 12 100%
repoze.bfg.push 14 14 100%
repoze.bfg.registry 64 64 100%
repoze.bfg.request 25 25 100%
repoze.bfg.router 154 154 100%
repoze.bfg.security 222 222 100%
repoze.bfg.settings 24 24 100%
repoze.bfg.template 6 6 100%
repoze.bfg.templating 17 17 100%
repoze.bfg.testing 227 227 100%
repoze.bfg.tests 0 0 100%
repoze.bfg.tests.fixtureapp 0 0 100%
repoze.bfg.tests.fixtureapp.models 3 3 100%
repoze.bfg.tests.fixtureapp.views 4 4 100%
repoze.bfg.tests.grokkedapp 5 5 100%
repoze.bfg.tests.routesapp 0 0 100%
repoze.bfg.tests.routesapp.models 3 3 100%
repoze.bfg.tests.routesapp.views 4 4 100%
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 127 127 100%
repoze.bfg.tests.test_location 39 39 100%
repoze.bfg.tests.test_log 11 11 100%
repoze.bfg.tests.test_lru 74 74 100%
repoze.bfg.tests.test_push 29 29 100%
repoze.bfg.tests.test_registry 112 112 100%
repoze.bfg.tests.test_request 31 31 100%
repoze.bfg.tests.test_router 697 697 100%
repoze.bfg.tests.test_security 646 646 100%
repoze.bfg.tests.test_settings 83 83 100%
repoze.bfg.tests.test_template 73 73 100%
repoze.bfg.tests.test_templating 45 45 100%
repoze.bfg.tests.test_testing 408 408 100%
repoze.bfg.tests.test_traversal 606 606 100%
repoze.bfg.tests.test_url 126 126 100%
repoze.bfg.tests.test_urldispatch 345 345 100%
repoze.bfg.tests.test_view 418 418 100%
repoze.bfg.tests.test_wsgi 164 164 100%
repoze.bfg.tests.test_zcml 620 620 100%
repoze.bfg.traversal 171 171 100%
repoze.bfg.url 43 43 100%
repoze.bfg.urldispatch 158 158 100%
repoze.bfg.view 76 76 100%
repoze.bfg.wsgi 43 43 100%
repoze.bfg.zcml 246 246 100%
--------------------------------------------------------------------
TOTAL 6860 6860 100%
----------------------------------------------------------------------
Ran 397 tests in 18.572s
OK
|
