introduction.rst

single: Agendaless Consulting single: Pylons single: Django single: Zope single: frameworks vs. libraries single: framework

Pyramid Introduction

Pyramid is a general, open source, Python web application development framework. Its primary goal is to make it easier for a Python developer to create 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.

Pyramid attempts to follow follow these design and engineering principles:

Simplicity

Pyramid takes a "pay only for what you eat" approach. You can get results even if you have only a partial understanding of Pyramid. 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 tries to solve only the 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 easier for us to maintain complete and up-to-date documentation. It is our goal that no aspect of Pyramid is undocumented.

Speed

Pyramid is designed to provide noticeably fast execution for common tasks such as templating and simple response generation. Although “hardware is cheap", 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.

single: Pylons single: repoze namespace package

What Is The Pylons Project?

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.

single: pyramid and other frameworks single: Zope single: Pylons single: Django single: MVC

Pyramid and Other Web Frameworks

The first release of Pyramid's predecessor (named repoze.bfg) was made in July of 2008. At the end of 2010, we changed the name of repoze.bfg to Pyramid. 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 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 declarative 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.