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.. index::
single: Agendaless Consulting
single: Pylons
single: Django
single: Zope
single: frameworks vs. libraries
single: framework
:mod:`repoze.bfg` Introduction
==============================
Most of the logic in a web application is completely
application-specific. For example, the content of a web page served
by one web application might be a representation of the contents of an
accounting ledger, while the content of of a web page served by
another might be a listing of songs. These applications probably
won't serve the same set of customers. However, both the
ledger-serving and song-serving applications can be written using
:mod:`repoze.bfg` because it is a very general open source Python web
*framework*. As a framework, the primary job of :mod:`repoze.bfg` is
to make it easier for a developer to create arbitrary web
applications.
.. sidebar:: Frameworks vs. Libraries
A *framework* differs from a *library* in one very important way:
library code is always *called* by code that you write, while a
framework always *calls* code that you write. Using a set of
libraries to create an application is usually easier than using a
framework initially, because you can choose to cede control to
library code you have not authored very selectively. But when you
use a framework, you are required to cede a greater portion of
control to code you have not authored: code that resides in the
framework itself. You needn't use a framework at all to create a
web application using Python. A rich set of libraries already
exists for the platform. In practice, however, using a framework
to create an application is often more practical than rolling your
own via a set of libraries if the framework provides a set of
facilities that fits your application requirements.
The first release of :mod:`repoze.bfg` was made in July of 2008.
Since its first release, we've tried to ensure that BFG maintains the
following attributes:
Simplicity
:mod:`repoze.bfg` attempts to be a *"pay only for what you eat"*
framework which delivers results even if you have only partial
knowledge. Other frameworks may 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 produce an application, and we try to keep
the core set of concepts you need to understand to a minimum.
A Sense of Fun
Developing a :mod:`repoze.bfg` application should not feel
"enterprisey". We like to keep things down-to-earth.
Minimalism
:mod:`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 :mod:`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 :mod:`repoze.bfg`.
Speed
:mod:`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.
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".
Trustability
:mod:`repoze.bfg` is developed conservatively and tested
exhaustively. *If it ain't tested, it's broke.* Every release of
:mod:`repoze.bfg` has 100% statement coverage via unit tests.
Openness
Like :term:`Python`, the :mod:`repoze.bfg` software is distributed
under a `permissive open source license
<http://repoze.org/license.html>`_.
This book usually refers to the framework by its full package name,
:mod:`repoze.bfg`. However, it is often referred to colloquially as
just "BFG" (the "repoze-dot" dropped) in conversation.
.. index::
single: repoze.bfg and other frameworks
single: Zope
single: Pylons
single: Django
single: MVC
:mod:`repoze.bfg` and Other Web Frameworks
------------------------------------------
:mod:`repoze.bfg` was inspired by :term:`Zope`, :term:`Pylons` and
:term:`Django`. As a result, :mod:`repoze.bfg` borrows several
concepts and features from each, combining them into a unique web
framework.
Features such as :term:`traversal` and easy extensibility trace their
origins back to :term:`Zope`. Like Zope applications,
:mod:`repoze.bfg` applications can be easily extended. 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: no fork of the
application is required.
The :mod:`repoze.bfg` concept of :term:`URL dispatch` is inspired by
the :term:`Routes` system used by :term:`Pylons`. Like 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 included only for convenience. In essence, it only supplies a
mechanism to map URLs to :term:`view` code, along with a set of
conventions for calling those views. You are free to use third-party
components that fit your needs in your applications.
Insofar as the term `model-view-controller
<http://en.wikipedia.org/wiki/Model–view–controller>`_ has been
claimed to represent a class of web frameworks, :mod:`repoze.bfg`
generally fits into this class. The concepts of :term:`view` and
:term:`model` are used by :mod:`repoze.bfg` as they would be by
Django.
.. sidebar:: You Say BFG is MVC, But Where's The Controller?
The :mod:`repoze.bfg` authors believe that the MVC pattern just
doesn't really fit the web very well. In a :mod:`repoze.bfg`
application, there are models, which store data, and views, which
present the data stored in models. However, no facility provided
by the framework actually maps to the concept of a "controller".
So :mod:`repoze.bfg` is actually an "MV" framework rather than an
"MVC" framework. "MVC", however, is close enough as a general
classification moniker for purposes of comparison with other web
frameworks.
Like :term:`Pylons`, but unlike :term:`Zope`, a :mod:`repoze.bfg`
application developer may use completely imperative code to perform
common framework configuration tasks such as adding a view or a route.
In Zope, :term:`ZCML` is typically required for similar purposes. In
:term:`Grok`, :term:`decorator` objects and class-level declarations
are used for this purpose. :mod:`repoze.bfg` *supports* :term:`ZCML`
and supports decorator-based configuration, but does not require
either. See :ref:`configuration_narr` for more information.
Also unlike :term:`Zope` and unlike other "full-stack" frameworks such
as :term:`Django`, :mod:`repoze.bfg` makes no assumptions about which
persistence mechanisms you should 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 assume that
you 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 encourage or discourage the decision.
.. index::
single: Repoze
single: Agendaless Consulting
pair: repoze; namespace package
What Is Repoze?
---------------
:mod:`repoze.bfg` is a member of the collection of software published
under the :term:`Repoze` "brand". :term:`Repoze` software is written
by :term:`Agendaless Consulting` and a community of contributors. The
`Repoze website <http://repoze.org>`_ describes the Repoze brand in
more detail. Software authored that uses this brand is usually placed
into a ``repoze`` namespace package. This namespace consists of a
number of packages. Each package is useful in isolation. The
``repoze`` namespace package represents that the software is written
by a notional community rather than representing a collection of
software that is meant to be used as a unit. For example, even though
``repoze.bfg`` shares the same namespace as another popular Repoze
package, ``repoze.who``, these two packages are otherwise unrelated
and can be used separately.
.. index::
single: repoze.zope2
single: Zope 3
single: Zope 2
|
