31. EXTENDING AN EXISTING PYRAMID APPLICATION

for such a pattern to work satisfactorily. Because Pyramid is not very “opinionated”, developers are able to use wildly different patterns and technologies to build an application. A given Pyramid application may happen to be reusable by a particular third party integrator, because the integrator and the original developer may share similar base technology choices (such as the use of a particular relational database or ORM). But the same application may not be reusable by a different developer, because he has made different technology choices which are incompatible with the original developer’s.

As a result, the concept of a “pluggable application” is left to layers built above Pyramid, such as a “CMS” layer or “application server” layer. Such layers are apt to provide the necessary “opinions” (such as mandating a storage layer, a templating system, and a structured, well-documented pattern of registering that certain URLs map to certain bits of code) which makes the concept of a “pluggable application” possible. “Pluggable applications”, thus, should not plug in to Pyramid itself but should instead plug into a system written atop Pyramid.

Although it does not provide for “pluggable applications”, Pyramid does provide a rich set of mechanisms which allows for the extension of a single existing application. Such features can be used by frameworks built using Pyramid as a base. All Pyramid applications may not be pluggable, but all Pyramid applications are extensible.

31.2 Rules for Building An Extensible Application

There is only one rule you need to obey if you want to build a maximally extensible Pyramid application: as a developer, you should factor any overrideable imperative configuration you’ve created into functions which can be used via pyramid.config.Configurator.include() rather than inlined as calls to methods of a Configurator within the main function in your application’s __init__.py. For example, rather than:

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from pyramid.config import Configurator

if __name__ == ’__main__’: config = Configurator()

config.add_view(’myapp.views.view1’, name=’view1’) config.add_view(’myapp.views.view2’, name=’view2’)

You should do move the calls to add_view outside of the (non-reusable) if __name__ == ’__main__’ block, and into a reusable function:

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from pyramid.config import Configurator

if __name__ == ’__main__’:

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