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Pyramid
is a general, open source, Python web application development framework. Its primary goal is to make it easier for a developer to create web applications. The type of application being created could be a spreadsheet, a corporate intranet, or a social networking platform; Pyramid's generality enables it to be used to build an unconstrained variety of web applications.
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 Pyramid's predecessor (named repoze.bfg
) was made in July of 2008. We have worked hard to ensure that Pyramid continues to follow the design and engineering principles that we consider to be the core characteristics of a successful framework:
- Simplicity
Pyramid
takes a "pay only for what you eat" approach. This means that you can get results even if you have only a partial understanding ofPyramid
. It doesn’t force you to use any particular technology to produce an application, and we try to keep the core set of concepts that you need to understand to a minimum.- Minimalism
Pyramid
concentrates on providing fast, high-quality solutions to the fundamental problems of creating a web application: the mapping of URLs to code, templating, security and serving static assets. We consider these to be the core activities that are common to nearly all web applications.- Documentation
Pyramid's minimalism means that it is relatively easy for us to maintain extensive and up-to-date documentation. It is our goal that no aspect of Pyramid remains undocumented.
- Speed
Pyramid
is designed to provide noticeably fast execution for common tasks such as templating and simple response generation. Although the “hardware is cheap” mantra may appear to offer a ready solution to speed problems, the limits of this approach become painfully evident when one finds him or herself responsible for managing a great many machines.- Reliability
Pyramid
is developed conservatively and tested exhaustively. Where Pyramid source code is concerned, our motto is: "If it ain’t tested, it’s broke". Every release of Pyramid has 100% statement coverage via unit tests.- Openness
As with Python, the Pyramid software is distributed under a permissive open source license.
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Pyramid
is a member of the collection of software published under the Pylons Project. Pylons software is written by a loose-knit community of contributors. The Pylons Project website includes details about how Pyramid
relates to the Pylons Project.
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Until the end of 2010, Pyramid
was known as repoze.bfg
; it was merged into the Pylons project as Pyramid
in November of that year.
Pyramid
was inspired by Zope
, Pylons
(version 1.0) and Django
. As a result, Pyramid
borrows several concepts and features from each, combining them into a unique web framework.
Many features of Pyramid
trace their origins back to Zope
. Like Zope applications, Pyramid
applications can be configured via a set of declarative configuration files. Like Zope applications, Pyramid
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 forking the original application. The concepts of traversal
and declarative security in Pyramid
were pioneered first in Zope.
The Pyramid
concept of URL dispatch
is inspired by the Routes
system used by Pylons
version 1.0. Like Pylons version 1.0, Pyramid
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 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.
The concept of view
is used by Pyramid
mostly as it would be by Django. Pyramid
has a documentation culture more like Django's than like Zope's.
Like Pylons
version 1.0, but unlike Zope
, a Pyramid
application developer may use completely imperative code to perform common framework configuration tasks such as adding a view or a route. In Zope, ZCML
is typically required for similar purposes. In Grok
, a Zope-based web framework, decorator
objects and class-level declarations are used for this purpose. Pyramid
supports ZCML
and decorator-based configuration, but does not require either. See configuration_narr
for more information.
Also unlike Zope
and unlike other "full-stack" frameworks such as Django
, Pyramid
makes no assumptions about which persistence mechanisms you should use to build an application. Zope applications are typically reliant on ZODB
; Pyramid
allows you to build ZODB
applications, but it has no reliance on the ZODB software. Likewise, Django
tends to assume that you want to store your application's data in a relational database. Pyramid
makes no such assumption; it allows you to use a relational database but doesn't encourage or discourage the decision.
Other Python web frameworks advertise themselves as members of a class of web frameworks named model-view-controller frameworks. Insofar as this term has been claimed to represent a class of web frameworks, Pyramid
also generally fits into this class.
You Say Pyramid
is MVC, But Where's The Controller?
The Pyramid
authors believe that the MVC pattern just doesn't really fit the web very well. In a Pyramid
application, there is a resource tree, which represents the site structure, and views, which tend to present the data stored in the resource tree and a user-defined "domain model". However, no facility provided by the framework actually necessarily maps to the concept of a "controller" or "model". So if you had to give it some acronym, I guess you'd say Pyramid
is actually an "RV" framework rather than an "MVC" framework. "MVC", however, is close enough as a general classification moniker for purposes of comparison with other web frameworks.