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:app:`Pyramid` Introduction

:app:`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 these design and engineering principles:

:app:`Pyramid` takes a "pay only for what you eat" approach. You can get results even if you have only a partial understanding of :app:`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.
:app:`Pyramid` tries to solve only 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.
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.
:app:`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.
:app:`Pyramid` is developed conservatively and tested exhaustively. Where Pyramid source code is concerned, our motto is: "If it ain’t tested, it’s broke".
As with Python, the Pyramid software is distributed under a permissive open source license.

What Makes Pyramid Unique

Understandably, people don't usually want to hear about squishy engineering principles, they want to hear about concrete stuff that solves their problems. With that in mind, what would make someone want to use Pyramid instead of one of the many other web frameworks available today? What makes Pyramid unique?

This is a hard question to answer, because there are lots of excellent choices, and it's actually quite hard to make a wrong choice, particularly in the Python web framework market. But one reasonable answer is this: you can write very small applications in Pyramid without needing to know a lot. "What?", you say, "that can't possibly be a unique feature, lots of other web frameworks let you do that!" Well, you're right. But unlike many other systems, you can also write very large applications in Pyramid if you learn a little more about it. Pyramid will allow you to become productive quickly, and will grow with you; it won't hold you back when your application is small and it won't get in your way when your application becomes large. "Well that's fine," you say, "lots of other frameworks let me write large apps too." Absolutely. But other Python web frameworks don't seamlessly let you do both. They seem to fall into two non-overlapping categories: frameworks for "small apps" and frameworks for "big apps". The "small app" frameworks typically sacrifice "big app" features, and vice versa.

We don't think it's a universally reasonable suggestion to write "small apps" in a "small framework" and "big apps" in a "big framework". You can't really know to what size every application will eventually grow. We don't really want to have to rewrite a previously small application in another framework when it gets "too big". We believe the current binary distinction between frameworks for small and large applications is just false; a well-designed framework should be able to be good at both. Pyramid strives to be that kind of framework.

To this end, Pyramid provides a set of features, that, combined, are unique amongst Python web frameworks. Lots of other frameworks contain some combination of these features; Pyramid of course actually stole many of them from those other frameworks. But Pyramid is the only one that has all of them in one place, documented appropriately, and useful a la carte without necessarily paying for the entire banquet. These are detailed below.

Single-file applications

You can write a Pyramid application that lives entirely in one Python file, not unlike existing Python microframeworks. This is beneficial for one-off prototyping, bug reproduction, and very small applications. These applications are easy to understand because all the information about the application lives in a single place, and you can deploy them without needing to understand much about Python distributions and packaging. Pyramid isn't really marketed as a microframework, but it allows you to do almost everything that frameworks that are marketed as micro offer in very similar ways.

See also :ref:`firstapp_chapter`.

Decorator-based configuration

If you like the idea of framework configuration statements living next to the code it configures, so you don't have to constantly switch between files to refer to framework configuration when adding new code, you can use Pyramid decorators to localize the configuration. For example:

from pyramid.view import view_config
from pyramid.response import Response

def fred_view(request):
    return Response('fred')

However, unlike some other systems, using decorators for Pyramid configuration does not make your application difficult to extend, test or reuse. The :class:`~pyramid.view.view_config` decorator, for example, does not actually change the input or output of the function it decorates, so testing it is a "WYSIWYG" operation; you don't need to understand the framework to test your own code, you just behave as if the decorator is not there. You can also instruct Pyramid to ignore some decorators, or use completely imperative configuration instead of decorators to add views. Pyramid decorators are inert instead of eager: you detect and activate them with a :term:`scan`.

Example: :ref:`mapping_views_using_a_decorator_section`.

URL generation

Pyramid is capable of generating URLs for resources, routes, and static assets. Its URL generation APIs are easy to use and flexible. If you use Pyramid's various APIs for generating URLs, you can change your configuration around arbitrarily without fear of breaking a link on one of your web pages.

Example: :ref:`generating_route_urls`.

Static file serving

Pyramid is perfectly willing to serve static files itself. It won't make you use some external web server to do that. You can even serve more than one set of static files in a single Pyramid web application (e.g. /static and /static2). You can also, optionally, place your files on an external web server and ask Pyramid to help you generate URLs to those files, so you can use Pyramid's internal fileserving while doing development, and a faster static file server in production without changing any code.

Example: :ref:`static_assets_section`.

Debug Toolbar

Pyramid's debug toolbar comes activated when you use a Pyramid scaffold to render a project. This toolbar overlays your application in the browser, and allows you access to framework data such as the routes configured, the last renderings performed, the current set of packages installed, SQLAlchemy queries run, logging data, and various other facts. When an exception occurs, you can use its interactive debugger to poke around right in your browser to try to determine the cause of the exception. It's handy.

Example: :ref:`debug_toolbar`.

Debugging settings

Pyramid has debugging settings that allow you to print Pyramid runtime information to the console when things aren't behaving as you're expecting. For example, you can turn on "debug_notfound", which prints an informative message to the console every time a URL does not match any view. You can turn on "debug_authorization", which lets you know why a view execution was allowed or denied by printing a message to the console. These features are useful for those WTF moments.

There are also a number of commands that you can invoke within a Pyramid environment that allow you to introspect the configuration of your system: proutes shows all configured routes for an application in the order they'll be evaluated for matching; pviews shows all configured views for any given URL. These are also WTF-crushers in some circumstances.

Examples: :ref:`debug_authorization_section` and :ref:`command_line_chapter`.


Pyramid has an extensive set of add-ons held to the same quality standards as the Pyramid core itself. Add-ons are packages which provide functionality that the Pyramid core doesn't. Add-on packages already exist which let you easily send email, let you use the Jinja2 templating system, let you use XML-RPC or JSON-RPC, let you integrate with jQuery Mobile, etc.


Class-based and function-based views

Pyramid has a structured, unified concept of a :term:`view callable`. View callables can be functions, methods of classes, or even instances. When you add a new view callable, you can choose to make it a function or a method of a class; in either case, Pyramid treats it largely the same way. You can change your mind later, and move code between methods of classes and functions. A collection of similar view callables can be attached to a single class as methods, if that floats your boat, and they can share initialization code as necessary. All kinds of views are easy to understand and use and operate similarly. There is no phony distinction between them; they can be used for the same purposes.

Here's a view callable defined as a function:

Here's a few views defined as methods of a class instead:

See also :ref:`view_config_placement`.

Asset specifications

Asset specifications are strings that contain both a Python package name and a file or directory name, e.g. MyPackage:static/index.html. Use of these specifications is omnipresent in Pyramid. An asset specification can refer to a template, a translation directory, or any other package-bound static resource. This makes a system built on Pyramid extensible, because you don't have to rely on globals ("the static directory") or lookup schemes ("the ordered set of template directories") to address your files. You can move files around as necessary, and include other packages that may not share your system's templates or static files without encountering conflicts.

Because asset specifications are used heavily in Pyramid, we've also provided a way to allow users to override assets. Say you love a system that someone else has created with Pyramid but you just need to change "that one template" to make it all better. No need to fork the application. Just override the asset specification for that template with your own inside a wrapper, and you're good to go.

Examples: :ref:`asset_specifications` and :ref:`overriding_assets_section`.

Extensible templating

Pyramid has a structured API that allows for pluggability of "renderers". Templating systems such as Mako, Genshi, Chameleon, and Jinja2 can be treated as renderers. Renderer bindings for all of these templating systems already exist for use in Pyramid. But if you'd rather use another, it's not a big deal. Just copy the code from an existing renderer package, and plug in your favorite templating system. You'll then be able to use that templating system from within Pyramid just as you'd use one of the "built-in" templating systems.

Pyramid does not make you use a single templating system exclusively. You can use multiple templating systems, even in the same project.

Example: :ref:`templates_used_directly`.

Rendered views can return dictionaries

If you use a :term:`renderer`, you don't have to return a special kind of "webby" Response object from a view. Instead, you can return a dictionary, and Pyramid will take care of converting that dictionary to a Response using a template on your behalf. This makes the view easier to test, because you don't have to parse HTML in your tests; just make an assertion instead that the view returns "the right stuff" in the dictionary it returns. You can write "real" unit tests instead of functionally testing all of your views.

For example, instead of:

You can do this:

When this view callable is called by Pyramid, the {'a':1} dictionary will be rendered to a response on your behalf. The string passed as renderer= above is an :term:`asset specification`. It is in the form packagename:directoryname/filename.ext. In this case, it refers to the file in the templates directory within the myapp Python package. Asset specifications are omnipresent in Pyramid: see :ref:`intro_asset_specs` for more information.

Example: :ref:`renderers_chapter`.

Event system

Pyramid emits events during its request processing lifecycle. You can subscribe any number of listeners to these events. For example, to be notified of a new request, you can subscribe to the NewRequest event. To be notified that a template is about to be rendered, you can subscribe to the BeforeRender event, and so forth. Using an event publishing system as a framework notification feature instead of hardcoded hook points tends to make systems based on that framework less brittle.

You can also use Pyramid's event system to send your own events. For example, if you'd like to create a system that is itself a framework, and may want to notify subscribers that a document has just been indexed, you can create your own event type (DocumentIndexed perhaps) and send the event via Pyramid. Users of this framework can then subscribe to your event like they'd subscribe to the events that are normally sent by Pyramid itself.

Example: :ref:`events_chapter` and :ref:`event_types`.

Built-in internationalization

Pyramid ships with internationalization-related features in its core: localization, pluralization, and creating message catalogs from source files and templates. Pyramid allows for a plurality of message catalog via the use of translation domains: you can create a system that has its own translations without conflict with other translations in other domains.

Example: :ref:`i18n_chapter`.

HTTP caching

Pyramid provides an easy way to associate views with HTTP caching policies. You can just tell Pyramid to configure your view with an http_cache statement, and it will take care of the rest:

@view_config(http_cache=3600) # 60 minutes
def myview(request): ....

Pyramid will add appropriate Cache-Control and Expires headers to responses generated when this view is invoked.

See the :meth:`~pyramid.config.Configurator.add_view` method's http_cache documentation for more information.


Pyramid has built-in HTTP sessioning. This allows you to associate data with otherwise anonymous users between requests. Lots of systems do this. But Pyramid also allows you to plug in your own sessioning system by creating some code that adheres to a documented interface. Currently there is a binding package for the third-party Beaker sessioning system that does exactly this. But if you have a specialized need (perhaps you want to store your session data in MongoDB), you can. You can even switch between implementations without changing your application code.

Example: :ref:`sessions_chapter`.


The Pyramid core is, as far as we can tell, at least marginally faster than any other existing Python web framework. It has been engineered from the ground up for speed. It only does as much work as absolutely necessary when you ask it to get a job done. Extraneous function calls and suboptimal algorithms in its core codepaths are avoided. It is feasible to get, for example, between 3500 and 4000 requests per second from a simple Pyramid view on commodity dual-core laptop hardware and an appropriate WSGI server (mod_wsgi or gunicorn). In any case, performance statistics are largely useless without requirements and goals, but if you need speed, Pyramid will almost certainly never be your application's bottleneck; at least no more than Python will be a bottleneck.


Exception views

Exceptions happen. Rather than deal with exceptions that might present themselves to a user in production in an ad-hoc way, Pyramid allows you to register an :term:`exception view`. Exception views are like regular Pyramid views, but they're only invoked when an exception "bubbles up" to Pyramid itself. For example, you might register an exception view for the :exc:`Exception` exception, which will catch all exceptions, and present a pretty "well, this is embarrassing" page. Or you might choose to register an exception view for only specific kinds of application-specific exceptions, such as an exception that happens when a file is not found, or an exception that happens when an action cannot be performed because the user doesn't have permission to do something. In the former case, you can show a pretty "Not Found" page; in the latter case you might show a login form.

Example: :ref:`exception_views`.

No singletons

Pyramid is written in such a way that it requires your application to have exactly zero "singleton" data structures. Or, put another way, Pyramid doesn't require you to construct any "mutable globals". Or put even a different way, an import of a Pyramid application needn't have any "import-time side effects". This is esoteric-sounding, but if you've ever tried to cope with parameterizing a Django "" file for multiple installations of the same application, or if you've ever needed to monkey-patch some framework fixture so that it behaves properly for your use case, or if you've ever wanted to deploy your system using an asynchronous server, you'll end up appreciating this feature. It just won't be a problem. You can even run multiple copies of a similar but not identically configured Pyramid application within the same Python process. This is good for shared hosting environments, where RAM is at a premium.

View predicates and many views per route

Unlike many other systems, Pyramid allows you to associate more than one view per route. For example, you can create a route with the pattern /items and when the route is matched, you can shuffle off the request to one view if the request method is GET, another view if the request method is POST, etc. A system known as "view predicates" allows for this. Request method matching is the very most basic thing you can do with a view predicate. You can also associate views with other request parameters such as the elements in the query string, the Accept header, whether the request is an XHR request or not, and lots of other things. This feature allows you to keep your individual views "clean"; they won't need much conditional logic, so they'll be easier to test.

Example: :ref:`view_configuration_parameters`.

Transaction management

Pyramid's :term:`scaffold` system renders projects that include a transaction management system, stolen from Zope. When you use this transaction management system, you cease being responsible for committing your data anymore. Instead, Pyramid takes care of committing: it commits at the end of a request or aborts if there's an exception. Why is that a good thing? Having a centralized place for transaction management is a great thing. If, instead of managing your transactions in a centralized place, you sprinkle session.commit calls in your application logic itself, you can wind up in a bad place. Wherever you manually commit data to your database, it's likely that some of your other code is going to run after your commit. If that code goes on to do other important things after that commit, and an error happens in the later code, you can easily wind up with inconsistent data if you're not extremely careful. Some data will have been written to the database that probably should not have. Having a centralized commit point saves you from needing to think about this; it's great for lazy people who also care about data integrity. Either the request completes successfully, and all changes are committed, or it does not, and all changes are aborted.

Also, Pyramid's transaction management system allows you to synchronize commits between multiple databases, and allows you to do things like conditionally send email if a transaction commits, but otherwise keep quiet.

Example: :ref:`bfg_sql_wiki_tutorial` (note the lack of commit statements anywhere in application code).

Configuration conflict detection

When a system is small, it's reasonably easy to keep it all in your head. But when systems grow large, you may have hundreds or thousands of configuration statements which add a view, add a route, and so forth. Pyramid's configuration system keeps track of your configuration statements, and if you accidentally add two that are identical, or Pyramid can't make sense out of what it would mean to have both statements active at the same time, it will complain loudly at startup time. It's not dumb though: it will automatically resolve conflicting configuration statements on its own if you use the configuration :meth:`~pyramid.config.Configurator.include` system: "more local" statements are preferred over "less local" ones. This allows you to intelligently factor large systems into smaller ones.

Example: :ref:`conflict_detection`.

Configuration extensibility

Unlike other systems, Pyramid provides a structured "include" mechanism (see :meth:`~pyramid.config.Configurator.include`) that allows you to combine applications from multiple Python packages. All the configuration statements that can be performed in your "main" Pyramid application can also be performed by included packages including the addition of views, routes, subscribers, and even authentication and authorization policies. You can even extend or override an existing application by including another application's configuration in your own, overriding or adding new views and routes to it. This has the potential to allow you to create a big application out of many other smaller ones. For example, if you want to reuse an existing application that already has a bunch of routes, you can just use the include statement with a route_prefix; the new application will live within your application at a URL prefix. It's not a big deal, and requires little up-front engineering effort.

For example:

See also :ref:`including_configuration` and :ref:`building_an_extensible_app`

Flexible authentication and authorization

Pyramid includes a flexible, pluggable authentication and authorization system. No matter where your user data is stored, or what scheme you'd like to use to permit your users to access your data, you can use a predefined Pyramid plugpoint to plug in your custom authentication and authorization code. If you want to change these schemes later, you can just change it in one place rather than everywhere in your code. It also ships with prebuilt well-tested authentication and authorization schemes out of the box. But what if you don't want to use Pyramid's built-in system? You don't have to. You can just write your own bespoke security code as you would in any other system.

Example: :ref:`enabling_authorization_policy`.


:term:`Traversal` is a concept stolen from :term:`Zope`. It allows you to create a tree of resources, each of which can be addressed by one or more URLs. Each of those resources can have one or more views associated with it. If your data isn't naturally treelike (or you're unwilling to create a treelike representation of your data), you aren't going to find traversal very useful. However, traversal is absolutely fantastic for sites that need to be arbitrarily extensible: it's a lot easier to add a node to a tree than it is to shoehorn a route into an ordered list of other routes, or to create another entire instance of an application to service a department and glue code to allow disparate apps to share data. It's a great fit for sites that naturally lend themselves to changing departmental hierarchies, such as content management systems and document management systems. Traversal also lends itself well to systems that require very granular security ("Bob can edit this document" as opposed to "Bob can edit documents").

Examples: :ref:`hello_traversal_chapter` and :ref:`much_ado_about_traversal_chapter`.


Pyramid has a sort of internal WSGI-middleware-ish pipeline that can be hooked by arbitrary add-ons named "tweens". The debug toolbar is a "tween", and the pyramid_tm transaction manager is also. Tweens are more useful than WSGI middleware in some circumstances because they run in the context of Pyramid itself, meaning you have access to templates and other renderers, a "real" request object, and other niceties.

Example: :ref:`registering_tweens`.

View response adapters

A lot is made of the aesthetics of what kinds of objects you're allowed to return from view callables in various frameworks. In a previous section in this document we showed you that, if you use a :term:`renderer`, you can usually return a dictionary from a view callable instead of a full-on :term:`Response` object. But some frameworks allow you to return strings or tuples from view callables. When frameworks allow for this, code looks slightly prettier, because fewer imports need to be done, and there is less code. For example, compare this:

To this:

The former is "prettier", right?

Out of the box, if you define the former view callable (the one that simply returns a string) in Pyramid, when it is executed, Pyramid will raise an exception. This is because "explicit is better than implicit", in most cases, and by default, Pyramid wants you to return a :term:`Response` object from a view callable. This is because there's usually a heck of a lot more to a response object than just its body. But if you're the kind of person who values such aesthetics, we have an easy way to allow for this sort of thing:

Do that once in your Pyramid application at startup. Now you can return strings from any of your view callables, e.g.:

Oh noes! What if you want to indicate a custom content type? And a custom status code? No fear:

Once this is done, both of these view callables will work:

Pyramid defaults to explicit behavior, because it's the most generally useful, but provides hooks that allow you to adapt the framework to localized aesthetic desires.

See also :ref:`using_iresponse`.

"Global" response object

"Constructing these response objects in my view callables is such a chore! And I'm way too lazy to register a response adapter, as per the prior section," you say. Fine. Be that way:

See also :ref:`request_response_attr`.

Automating repetitive configuration

Does Pyramid's configurator allow you to do something, but you're a little adventurous and just want it a little less verbose? Or you'd like to offer up some handy configuration feature to other Pyramid users without requiring that we change Pyramid? You can extend Pyramid's :term:`Configurator` with your own directives. For example, let's say you find yourself calling :meth:`pyramid.config.Configurator.add_view` repetitively. Usually you can take the boring away by using existing shortcuts, but let's say that this is a case such a way that no existing shortcut works to take the boring away:

Pretty tedious right? You can add a directive to the Pyramid configurator to automate some of the tedium away:

Once that's done, you can call the directive you've just added as a method of the Configurator object:

Your previously repetitive configuration lines have now morphed into one line.

You can share your configuration code with others this way too by packaging it up and calling :meth:`~pyramid.config.Configurator.add_directive` from within a function called when another user uses the :meth:`~pyramid.config.Configurator.include` method against your code.

See also :ref:`add_directive`.

Programmatic Introspection

If you're building a large system that other users may plug code into, it's useful to be able to get an enumeration of what code they plugged in at application runtime. For example, you might want to show them a set of tabs at the top of the screen based on an enumeration of views they registered.

This is possible using Pyramid's :term:`introspector`.

Here's an example of using Pyramid's introspector from within a view callable:

See also :ref:`using_introspection`.

Python 3 Compatibility

Pyramid and most of its add-ons are Python 3 compatible. If you develop a Pyramid application today, you won't need to worry that five years from now you'll be backwatered because there are language features you'd like to use but your framework doesn't support newer Python versions.


Every release of Pyramid has 100% statement coverage via unit and integration tests, as measured by the coverage tool available on PyPI. It also has greater than 95% decision/condition coverage as measured by the instrumental tool available on PyPI. It is automatically tested by the Jenkins tool on Python 2.6, Python 2.7, Python 3.2 and PyPy after each commit to its GitHub repository. Official Pyramid add-ons are held to a similar testing standard. We still find bugs in Pyramid and its official add-ons, but we've noticed we find a lot more of them while working on other projects that don't have a good testing regime.



It's our goal that no Pyramid question go unanswered. Whether you ask a question on IRC, on the Pylons-discuss maillist, or on StackOverflow, you're likely to get a reasonably prompt response. We don't tolerate "support trolls" or other people who seem to get their rocks off by berating fellow users in our various offical support channels. We try to keep it well-lit and new-user-friendly.

Example: Visit irc:// (the #pyramid channel on in an IRC client) or the pylons-discuss maillist at .


It's a constant struggle, but we try to maintain a balance between completeness and new-user-friendliness in the official narrative Pyramid documentation (concrete suggestions for improvement are always appreciated, by the way). We also maintain a "cookbook" of recipes, which are usually demonstrations of common integration scenarios, too specific to add to the official narrative docs. In any case, the Pyramid documentation is comprehensive.

Example: The rest of this documentation and the cookbook at .

What Is The Pylons Project?

:app:`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 :app:`Pyramid` relates to the Pylons Project.

:app:`Pyramid` and Other Web Frameworks

The first release of Pyramid's predecessor (named :mod:`repoze.bfg`) was made in July of 2008. At the end of 2010, we changed the name of :mod:`repoze.bfg` to :app:`Pyramid`. It was merged into the Pylons project as :app:`Pyramid` in November of that year.

:app:`Pyramid` was inspired by :term:`Zope`, :term:`Pylons` (version 1.0) and :term:`Django`. As a result, :app:`Pyramid` borrows several concepts and features from each, combining them into a unique web framework.

Many features of :app:`Pyramid` trace their origins back to :term:`Zope`. Like Zope applications, :app:`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 :term:`traversal` and declarative security in :app:`Pyramid` were pioneered first in Zope.

The :app:`Pyramid` concept of :term:`URL dispatch` is inspired by the :term:`Routes` system used by :term:`Pylons` version 1.0. Like Pylons version 1.0, :app:`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 :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.

The concept of :term:`view` is used by :app:`Pyramid` mostly as it would be by Django. :app:`Pyramid` has a documentation culture more like Django's than like Zope's.

Like :term:`Pylons` version 1.0, but unlike :term:`Zope`, a :app:`Pyramid` 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`, a Zope-based web framework, :term:`decorator` objects and class-level declarations are used for this purpose. Out of the box, Pyramid supports imperative and decorator-based configuration; :term:`ZCML` may be used via an add-on package named pyramid_zcml.

Also unlike :term:`Zope` and unlike other "full-stack" frameworks such as :term:`Django`, :app:`Pyramid` makes no assumptions about which persistence mechanisms you should use to build an application. Zope applications are typically reliant on :term:`ZODB`; :app:`Pyramid` allows you to build :term:`ZODB` applications, but it has no reliance on the ZODB software. Likewise, :term:`Django` tends to assume that you want to store your application's data in a relational database. :app:`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, :app:`Pyramid` also generally fits into this class.

You Say :app:`Pyramid` is MVC, But Where's The Controller?

The :app:`Pyramid` authors believe that the MVC pattern just doesn't really fit the web very well. In a :app:`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 :app:`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.

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