What's New in Pyramid 1.4

This article explains the new features in Pyramid version 1.4 as compared to its predecessor, Pyramid 1.3. It also documents backwards incompatibilities between the two versions and deprecations added to Pyramid 1.4, as well as software dependency changes and notable documentation additions.

Major Feature Additions

The major feature additions in Pyramid 1.4 follow.

Third-Party Predicates

  • Third-party custom view, route, and subscriber predicates can now be added for use by view authors via pyramid.config.Configurator.add_view_predicate(), pyramid.config.Configurator.add_route_predicate() and pyramid.config.Configurator.add_subscriber_predicate(). So, for example, doing this:

    config.add_view_predicate('abc', my.package.ABCPredicate)

    Might allow a view author to do this in an application that configured that predicate:

    @view_config(abc=1)

    Similar features exist for pyramid.config.Configurator.add_route(), and pyramid.config.Configurator.add_subscriber(). See Adding a Custom View, Route, or Subscriber Predicate for more information.

Easy Custom JSON Serialization

  • Views can now return custom objects which will be serialized to JSON by a JSON renderer by defining a __json__ method on the object's class. This method should return values natively serializable by json.dumps (such as ints, lists, dictionaries, strings, and so forth). See Serializing Custom Objects for more information. The JSON renderer now also allows for the definition of custom type adapters to convert unknown objects to JSON serializations, in case you can't add a __json__ method to returned objects.

Partial Mako and Chameleon Template Renderings

  • The Mako renderer now supports using a def name in an asset spec. When the def name is present in the asset spec, the system will render the template named def within the template instead of rendering the entire template. An example asset spec which names a def is package:path/to/template#defname.mako. This will render the def named defname inside the template.mako template instead of rendering the entire template. The old way of returning a tuple in the form ('defname', {}) from the view is supported for backward compatibility.

  • The Chameleon ZPT renderer now supports using a macro name in an asset spec. When the macro name is present in the asset spec, the system will render the macro listed as a define-macro and return the result instead of rendering the entire template. An example asset spec: package:path/to/template#macroname.pt. This will render the macro defined as macroname within the template.pt template instead of the entire template.

Subrequest Support

Minor Feature Additions

  • pyramid.authentication.AuthTktAuthenticationPolicy has been updated to support newer hashing algorithms such as sha512. Existing applications should consider updating if possible for improved security over the default md5 hashing.

  • pyramid.config.Configurator.add_directive() now accepts arbitrary callables like partials or objects implementing __call__ which don't have __name__ and __doc__ attributes. See https://github.com/Pylons/pyramid/issues/621 and https://github.com/Pylons/pyramid/pull/647.

  • As of this release, the request_method view/route predicate, when used, will also imply that HEAD is implied when you use GET. For example, using @view_config(request_method='GET') is equivalent to using @view_config(request_method=('GET', 'HEAD')). Using @view_config(request_method=('GET', 'POST') is equivalent to using @view_config(request_method=('GET', 'HEAD', 'POST'). This is because HEAD is a variant of GET that omits the body, and WebOb has special support to return an empty body when a HEAD is used.

  • pyramid.config.Configurator.add_request_method() has been introduced to support extending request objects with arbitrary callables. This method expands on the now documentation-deprecated pyramid.config.Configurator.set_request_property() by supporting methods as well as properties. This method also causes less code to be executed at request construction time than set_request_property().

  • The static view machinery now raises rather than returns pyramid.httpexceptions.HTTPNotFound and pyramid.httpexceptions.HTTPMovedPermanently exceptions, so these can be caught by the Not Found View (and other exception views).

  • When there is a predicate mismatch exception (seen when no view matches for a given request due to predicates not working), the exception now contains a textual description of the predicate which didn't match.

  • An pyramid.config.Configurator.add_permission() directive method was added to the Configurator. This directive registers a free-standing permission introspectable into the Pyramid introspection system. Frameworks built atop Pyramid can thus use the permissions introspectable category data to build a comprehensive list of permissions supported by a running system. Before this method was added, permissions were already registered in this introspectable category as a side effect of naming them in an pyramid.config.Configurator.add_view() call, this method just makes it possible to arrange for a permission to be put into the permissions introspectable category without naming it along with an associated view. Here's an example of usage of add_permission:

    config = Configurator()
config.add_permission('view')

  • The pyramid.session.UnencryptedCookieSessionFactoryConfig() function now accepts signed_serialize and signed_deserialize hooks which may be used to influence how the sessions are marshalled (by default this is done with HMAC+pickle).

  • pyramid.testing.DummyRequest now supports methods supplied by the pyramid.util.InstancePropertyMixin class such as set_property.

  • Request properties and methods added via pyramid.config.Configurator.add_request_method() or pyramid.config.Configurator.set_request_property() are now available to tweens.

  • Request properties and methods added via pyramid.config.Configurator.add_request_method() or pyramid.config.Configurator.set_request_property() are now available in the request object returned from pyramid.paster.bootstrap().

  • request.context of environment request during pyramid.paster.bootstrap() is now the root object if a context isn't already set on a provided request.

  • pyramid.decorator.reify is now an API, and was added to the API documentation.

  • Added the pyramid.testing.testConfig() context manager, which can be used to generate a configurator in a test, e.g. with testing.testConfig(...):.

  • A new pyramid.session.check_csrf_token() convenience API function was added.

  • A check_csrf view predicate was added. For example, you can now do config.add_view(someview, check_csrf=True). When the predicate is checked, if the csrf_token value in request.params matches the csrf token in the request's session, the view will be permitted to execute. Otherwise, it will not be permitted to execute.

  • Add Base.metadata.bind = engine to alchemy scaffold, so that tables defined imperatively will work.

  • Comments with references to documentation sections placed in scaffold .ini files.

  • Allow multiple values to be specified to the request_param view/route predicate as a sequence. Previously only a single string value was allowed. See https://github.com/Pylons/pyramid/pull/705

  • Added an HTTP Basic authentication policy at pyramid.authentication.BasicAuthAuthenticationPolicy.

  • The pyramid.config.Configurator.testing_securitypolicy() method now returns the policy object it creates.

  • The DummySecurityPolicy created by pyramid.config.Configurator.testing_securitypolicy() now sets a forgotten value on the policy (the value True) when its forget method is called.

  • The DummySecurityPolicy created by pyramid.config.Configurator.testing_securitypolicy() now sets a remembered value on the policy, which is the value of the principal argument it's called with when its remember method is called.

  • New physical_path view predicate. If specified, this value should be a string or a tuple representing the physical traversal path of the context found via traversal for this predicate to match as true. For example: physical_path='/' or physical_path='/a/b/c' or physical_path=('', 'a', 'b', 'c'). It's useful when you want to always potentially show a view when some object is traversed to, but you can't be sure about what kind of object it will be, so you can't use the context predicate.

  • Added an effective_principals route and view predicate.

  • Do not allow the userid returned from the pyramid.security.authenticated_userid() or the userid that is one of the list of principals returned by pyramid.security.effective_principals() to be either of the strings system.Everyone or system.Authenticated when any of the built-in authorization policies that live in pyramid.authentication are in use. These two strings are reserved for internal usage by Pyramid and they will no longer be accepted as valid userids.

  • Allow a _depth argument to pyramid.view.view_config, which will permit limited composition reuse of the decorator by other software that wants to provide custom decorators that are much like view_config.

  • Allow an iterable of decorators to be passed to pyramid.config.Configurator.add_view(). This allows views to be wrapped by more than one decorator without requiring combining the decorators yourself.

  • pyramid.security.view_execution_permitted() used to return True if no view could be found. It now raises a TypeError exception in that case, as it doesn't make sense to assert that a nonexistent view is execution-permitted. See https://github.com/Pylons/pyramid/issues/299.

  • Small microspeed enhancement which anticipates that a pyramid.response.Response object is likely to be returned from a view. Some code is shortcut if the class of the object returned by a view is this class. A similar microoptimization was done to pyramid.request.Request.is_response().

  • Make it possible to use variable arguments on all p* commands (pserve, pshell, pviews, etc) in the form a=1 b=2 so you can fill in values in parameterized .ini file, e.g. pshell etc/development.ini http_port=8080.

  • In order to allow people to ignore unused arguments to subscriber callables and to normalize the relationship between event subscribers and subscriber predicates, we now allow both subscribers and subscriber predicates to accept only a single event argument even if they've been subscribed for notifications that involve multiple interfaces.

Backwards Incompatibilities

  • The Pyramid router no longer adds the values bfg.routes.route or bfg.routes.matchdict to the request's WSGI environment dictionary. These values were docs-deprecated in repoze.bfg 1.0 (effectively seven minor releases ago). If your code depended on these values, use request.matched_route and request.matchdict instead.

  • It is no longer possible to pass an environ dictionary directly to pyramid.traversal.ResourceTreeTraverser.__call__ (aka ModelGraphTraverser.__call__). Instead, you must pass a request object. Passing an environment instead of a request has generated a deprecation warning since Pyramid 1.1.

  • Pyramid will no longer work properly if you use the webob.request.LegacyRequest as a request factory. Instances of the LegacyRequest class have a request.path_info which return a string. This Pyramid release assumes that request.path_info will unconditionally be Unicode.

  • The functions from pyramid.chameleon_zpt and pyramid.chameleon_text named get_renderer, get_template, render_template, and render_template_to_response have been removed. These have issued a deprecation warning upon import since Pyramid 1.0. Use pyramid.renderers.get_renderer(), pyramid.renderers.get_renderer().implementation(), pyramid.renderers.render() or pyramid.renderers.render_to_response() respectively instead of these functions.

  • The pyramid.configuration module was removed. It had been deprecated since Pyramid 1.0 and printed a deprecation warning upon its use. Use pyramid.config instead.

  • The pyramid.paster.PyramidTemplate API was removed. It had been deprecated since Pyramid 1.1 and issued a warning on import. If your code depended on this, adjust your code to import pyramid.scaffolds.PyramidTemplate instead.

  • The pyramid.settings.get_settings() API was removed. It had been printing a deprecation warning since Pyramid 1.0. If your code depended on this API, use pyramid.threadlocal.get_current_registry().settings instead or use the settings attribute of the registry available from the request (request.registry.settings).

  • These APIs from the pyramid.testing module were removed. They have been printing deprecation warnings since Pyramid 1.0:

  • In Pyramid 1.3 and previous, the __call__ method of a Response object returned by a view was invoked before any finished callbacks were executed. As of this release, the __call__ method of a Response object is invoked after finished callbacks are executed. This is in support of the pyramid.request.Request.invoke_subrequest() feature.

Deprecations

  • The pyramid.config.Configurator.set_request_property() directive has been documentation-deprecated. The method remains usable but the more featureful pyramid.config.Configurator.add_request_method() should be used in its place (it has all of the same capabilities but can also extend the request object with methods).

  • pyramid.authentication.AuthTktAuthenticationPolicy will emit a deprecation warning if an application is using the policy without explicitly passing a hashalg argument. This is because the default is "md5" which is considered theoretically subject to collision attacks. If you really want "md5" then you must specify it explicitly to get rid of the warning.

Documentation Enhancements

  • Added an Upgrading Pyramid chapter to the narrative documentation. It describes how to cope with deprecations and removals of Pyramid APIs and how to show Pyramid-generated deprecation warnings while running tests and while running a server.

  • Added a Invoking a Subrequest chapter to the narrative documentation.

  • All of the tutorials that use pyramid.authentication.AuthTktAuthenticationPolicy now explicitly pass sha512 as a hashalg argument.

  • Many cleanups and improvements to narrative and API docs.

Dependency Changes

  • Pyramid now requires WebOb 1.2b3+ (the prior Pyramid release only relied on 1.2dev+). This is to ensure that we obtain a version of WebOb that returns request.path_info as text.