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What's New In repoze.bfg 1.3

This article explains the new features in repoze.bfg version 1.3 as compared to the previous 1.2 release. It also documents backwards incompatibilities between the two versions and deprecations added to 1.3, as well as software dependency changes and notable documentation additions.

Major Feature Additions

The major feature additions in 1.3 are:

  • Internationalization (i18n) and localization (l10n) services
  • Exception views

Internationalization and Localization

repoze.bfg 1.3 offers internationalization (i18n) and localization (l10n) subsystems that can be used to translate the text of buttons, the text of error messages and other software- and template-defined values into the native language of a user of your application.

repoze.bfg i18n / l10n framework includes:

  • Support for translation string specifications.
  • Tools allowing you to specify and work with gettext message catalog files to allow for text translation.
  • Locale name negotiation features.
  • Translation and pluralization services.

For detailed documentation about repoze.bfg internationalization and localization features, see i18n_chapter.

Exception Views

In repoze.bfg 1.3+, when you use an exception (anything that inherits from the Python Exception builtin) as view context argument, e.g.:

from repoze.bfg.view import bfg_view
from repoze.bfg.exceptions import NotFound
from webob.exc import HTTPNotFound

@bfg_view(context=NotFound)
def notfound_view(request):
    return HTTPNotFound()

For the above example, when the repoze.bfg.exceptions.NotFound exception is raised by any view or any root factory, the notfound_view view callable will be invoked and its response returned.

Other normal view predicates can also be used in combination with an exception view registration:

from repoze.bfg.view import bfg_view
from repoze.bfg.exceptions import NotFound
from webob.exc import HTTPNotFound

@bfg_view(context=NotFound, route_name='home')
def notfound_view(request):
    return HTTPNotFound()

The above exception view names the route_name of home, meaning that it will only be called when the route matched has a name of home. You can therefore have more than one exception view for any given exception in the system: the "most specific" one will be called when the set of request circumstances match the view registration. The only predicate that cannot be not be used successfully is name. The name used to look up an exception view is always the empty string.

Existing (pre-1.3) normal views registered against objects inheriting from Exception will continue to work. Exception views used for user-defined exceptions and system exceptions used as contexts will also work.

The feature can be used with any view registration mechanism (@bfg_view decorator, ZCML, or imperative repoze.bfg.configuration.Configurator.add_view styles).

This feature was kindly contributed by Andrey Popp.

Minor Feature Additions

  • Use Venusian to perform @bfg_view decorator scanning rather than relying on a BFG-internal decorator scanner. This means that user-defined decorators can be defined and found during repoze.bfg scanning. See registering_configuration_decorators for more information.
  • It is now possible to turn on Chameleon template "debugging mode" for all Chameleon BFG templates by setting a BFG-related Paster .ini file setting named debug_templates. The exceptions raised by Chameleon templates when a rendering fails are sometimes less than helpful. debug_templates allows you to configure your application development environment so that exceptions generated by Chameleon during template compilation and execution will contain more helpful debugging information. This mode is on by default in newly generated projects. See also debug_templates_section.
  • A new API method named repoze.bfg.configuration.Configurator.derive_view was added. This API can be used to generate a BFG view callable from a user-supplied function, instance, or class. This useful for external framework and plugin authors wishing to wrap callables supplied by their users which follow the same calling conventions and response conventions as objects that can be supplied directly to BFG as a view callable.
  • Prior to 1.3, a route predicate had no access to route pattern matching information and had no way to know which route was matched. As of 1.3a4, each of the predicate callables fed to the custom_predicates argument of repoze.bfg.configuration.Configurator.add_route or the custom_predicates ZCML attribute can be a callable accepting two arguments. The first argument passed to a custom predicate is a dictionary conventionally named info. The second argument is the current request object. The info dictionary has a number of contained values: match is a dictionary: it represents the arguments matched in the URL by the route. route is an object representing the route which was matched. See also custom_route_predicates. In prior versions, the info argument was always None.
  • The repoze.bfg.url.route_url API has changed. If a keyword _app_url is present in the arguments passed to route_url, this value will be used as the protocol/hostname/port/leading path prefix of the generated URL. For example, using an _app_url of http://example.com:8080/foo would cause the URL http://example.com:8080/foo/fleeb/flub to be returned from this function if the expansion of the route pattern associated with the route_name expanded to /fleeb/flub.
  • It is now possible to use a URL as the name argument fed to repoze.bfg.configuration.Configurator.add_static_view. When the name argument is a URL, the repoze.bfg.url.static_url API will generate join this URL (as a prefix) to a path including the static file name. This makes it more possible to put static media on a separate webserver for production, while keeping static media package-internal and served by the development webserver during development.
  • New argument to repoze.bfg.configuration.Configurator.add_route and the ZCML route directive: traverse. If you would like to cause the context to be something other than the root object when this route matches, you can spell a traversal pattern as the traverse argument. This traversal pattern will be used as the traversal path: traversal will begin at the root object implied by this route (either the global root, or the object returned by the factory associated with this route). See repoze.bfg.configuration.Configurator.add_route for more information (the traverse argument).
  • A new method exists: repoze.bfg.configuration.Configurator.set_request_factory. If used, this method will set the factory used by the repoze.bfg router to create all request objects.
  • The repoze.bfg.configuration.Configurator constructor takes an additional argument: request_factory. If used, this argument will set the factory used by the repoze.bfg router to create all request objects.
  • The repoze.bfg.configuration.Configurator constructor takes an additional argument: request_factory. If used, this argument will set the factory used by the repoze.bfg router to create all request objects.
  • A new method exists repoze.bfg.configuration.Configurator.set_renderer_globals_factory. If used, this method will set the factory used by the repoze.bfg router to create renderer globals.
  • A new method exists: repoze.bfg.configuration.Configurator.get_settings. If used, this method will return the current settings object (performs the same job as the repoze.bfg.settings.get_settings API).
  • The repoze.bfg.configuration.Configurator constructor takes an additional argument: renderer_globals_factory. If used, this argument will set the factory used by the repoze.bfg router to create renderer globals.
  • Add repoze.bfg.renderers.render, repoze.bfg.renderers.render_to_response and repoze.bfg.renderers.get_renderer functions. These are imperative APIs which will use the same rendering machinery used by view configurations with a renderer= attribute/argument to produce a rendering or renderer. Because these APIs provide a central API for all rendering, they now form the preferred way to perform imperative template rendering. Using functions named render_* from modules such as repoze.bfg.chameleon_zpt and repoze.bfg.chameleon_text is now discouraged (although not deprecated). The code the backing older templating-system-specific APIs now calls into the newer repoze.bfg.renderer code.
  • The repoze.bfg.configuration.Configurator.testing_add_template method has been renamed to repoze.bfg.configuration.Configurator.testing_add_renderer. A backwards compatibility alias is present using the old name.
  • When decoding a URL segment to Unicode fails, the exception raised is now repoze.bfg.exceptions.URLDecodeError instead of UnicodeDecodeError. This makes it possible to register an exception view invoked specifically when repoze.bfg cannot decode a URL.
  • A repoze.bfg.events.subscriber decorator was added. This decorator can be used to decorates module-scope functions, which are then treated as event listeners after a scan() is performed. See the events_chapter documentation chapter and the repoze.bfg.events module documentation for more information.
  • The repoze.bfg.configuration.Configurator.add_route API now returns the route object that was added.

  • New API class: repoze.bfg.view.AppendSlashNotFoundViewFactory.

    There can only be one Not Found view in any repoze.bfg application. Even if you use :func:`repoze.bfg.view.append_slash_notfound_view as the Not Found view, repoze.bfg still must generate a 404 Not Found response when it cannot redirect to a slash-appended URL; this not found response will be visible to site users.

    If you don't care what this 404 response looks like, and only you need redirections to slash-appended route URLs, you may use the repoze.bfg.view.append_slash_notfound_view object as the Not Found view. However, if you wish to use a custom notfound view callable when a URL cannot be redirected to a slash-appended URL, you may wish to use an instance of the repoze.bfg.view.AppendSlashNotFoundViewFactory class as the Not Found view, supplying a view callable to be used as the custom notfound view as the first argument to its constructor. For instance:

    from repoze.bfg.exceptions import NotFound
from repoze.bfg.view import AppendSlashNotFoundViewFactory

def notfound_view(context, request):
    return HTTPNotFound('It aint there, stop trying!')

custom_append_slash = AppendSlashNotFoundViewFactory(notfound_view)
config.add_view(custom_append_slash, context=NotFound)

    The notfound_view supplied must adhere to the two-argument view callable calling convention of (context, request) (context will be the exception object).

Backwards Incompatibilities

  • In previous releases, when a URL could not be decoded from UTF-8 during traversal, a TypeError was raised. Now the error which is raised is repoze.bfg.exceptions.URLDecodeError.

  • A new internal exception class (not an API) named repoze.bfg.exceptions.PredicateMismatch now exists. This exception is currently raised when no constituent view of a multiview can be called (due to no predicate match). Previously, in this situation, a repoze.bfg.exceptions.NotFound exception was raised. We provide backwards compatibility for code that expected a NotFound to be raised when no predicates match by causing repoze.bfg.exceptions.PredicateMismatch to inherit from NotFound. This will cause any exception view registered for NotFound to be called when a predicate mismatch occurs, as was the previous behavior.

    There is however, one perverse case that will expose a backwards incompatibility. If 1) you had a view that was registered as a member of a multiview 2) this view explicitly raised a NotFound exception in order to proceed to the next predicate check in the multiview, that code will now behave differently: rather than skipping to the next view match, a NotFound will be raised to the top-level exception handling machinery instead. For code to be depending upon the behavior of a view raising NotFound to proceed to the next predicate match, would be tragic, but not impossible, given that NotFound is a public interface. repoze.bfg.exceptions.PredicateMismatch is not a public API and cannot be depended upon by application code, so you should not change your view code to raise PredicateMismatch. Instead, move the logic which raised the NotFound exception in the view out into a custom view predicate.

  • If, when you run your application's unit test suite under BFG 1.3, a KeyError naming a template or a ValueError indicating that a 'renderer factory' is not registered may is raised (e.g. ValueError: No factory for renderer named '.pt' when looking up karl.views:templates/snippets.pt), you may need to perform some extra setup in your test code.

    The best solution is to use the repoze.bfg.configuration.Configurator.testing_add_renderer (or, alternately the deprecated repoze.bfg.testing.registerTemplateRenderer or repoze.bfg.testing.registerDummyRenderer) API within the code comprising each individual unit test suite to register a "dummy" renderer for each of the templates and renderers used by code under test. For example:

    config = Configurator()
config.testing_add_renderer('karl.views:templates/snippets.pt')

    This will register a basic dummy renderer for this particular missing template. The repoze.bfg.configuration.Configurator.testing_add_renderer API actually returns the renderer, but if you don't care about how the render is used, you don't care about having a reference to it either.

    A more rough way to solve the issue exists. It causes the "real" template implementations to be used while the system is under test, which is suboptimal, because tests will run slower, and unit tests won't actually be unit tests, but it is easier. Always ensure you call the repoze.bfg.configuration.Configurator.setup_registry method. For example:

    reg = MyRegistry()
config = Configurator(registry=reg)
config.setup_registry()

    Calling repoze.bfg.configuration.Configurator.setup_registry only has an effect if you're passing in a registry argument to the Configurator constructor. setup_registry is called by the course of normal operations anyway if you do not pass in a registry.

    If your test suite isn't using a Configurator yet, and is still using the older repoze.bfg.testing APIs name repoze.bfg.testng.setUp or repoze.bfg.testng.cleanUp, these will register the renderers on your behalf.

    A variant on the symptom for this theme exists: you may already be dutifully registering a dummy template or renderer for a template used by the code you're testing using repoze.bfg.configuration.Configurator.testing_register_renderer or repoze.bfg.testing.registerTemplateRenderer, but (perhaps unbeknownst to you) the code under test expects to be able to use a "real" template renderer implementation to retrieve or render another template that you forgot was being rendered as a side effect of calling the code you're testing. This happened to work because it found the real template while the system was under test previously, and now it cannot. The solution is the same.

    It may also help reduce confusion to use a resource specification to specify the template path in the test suite and code rather than a relative path in either. A resource specification is unambiguous, while a relative path needs to be relative to "here", where "here" isn't always well-defined ("here" in a test suite may or may not be the same as "here" in the code under test).

  • A bug existed in the regular expression to do URL matching. As an example, the URL matching machinery would cause the pattern /{foo} to match the root URL / resulting in a match dictionary of {'foo':u''} or the pattern /{fud}/edit might match the URL//editresulting in a match dictionary of{'fud':u''}. It was always the intent that:segment`` markers in the pattern would need to match at least one character, and never match the empty string. This, however, means that in certain circumstances, a routing match which your application inadvertently depended upon may no longer happen.

Deprecations and Behavior Differences

  • The exception views feature replaces the need for the set_notfound_view and set_forbidden_view methods of the repoze.bfg.configuration.Configurator as well as the notfound_directive and forbidden_directive ZCML directives. Those methods and directives will continue to work for the foreseeable future, but they are deprecated in the documentation.
  • The repoze.bfg.renderers.rendered_response function was never an official API, but may have been imported by extensions in the wild. It is officially deprecated in this release. Use repoze.bfg.renderers.render_to_response instead.

  • The following APIs are documentation deprecated (meaning they are officially deprecated in documentation but do not raise a deprecation error upon their usage, and may continue to work for an indefinite period of time):

    In the repoze.bfg.chameleon_zpt module: get_renderer, get_template, render_template, render_template_to_response. The suggested alternatives are documented within the docstrings of those methods (which are still present in the documentation).

    In the repoze.bfg.chameleon_text module: get_renderer, get_template, render_template, render_template_to_response. The suggested alternatives are documented within the docstrings of those methods (which are still present in the documentation).

    In general, to perform template-related functions, one should now use the various methods in the repoze.bfg.renderers module.

Dependency Changes

  • A new install-time dependency on the venusian distribution was added.
  • A new install-time dependency on the translationstring distribution was added (internationalization).
  • Chameleon 1.2.3 or better is now required (internationalization and per-template debug settings).

Documentation Enhancements

  • Exception view documentation was added to the hooks_chapter narrative chapter.
  • A new narrative chapter entitled i18n_chapter was added.
  • The environment_chapter chapter was changed: documentation about the default_locale_name setting was added.
  • A new API chapter for the i18n_module module was added.
  • Documentation for the new translationdir_directive and localenegotiator_directive ZCML directives were added.
  • A section custom_route_predicates was added to the URL Dispatch narrative chapter.
  • The static_resources_section and generating_static_resource_urls sections of the Static Resources chapter have been updated to mention using repoze.bfg.url.static_url to generate URLs to external webservers.
  • Documentation for registering a new configuration decorator was added in registering_configuration_decorators.
  • The authorization chapter of the bfg_wiki_tutorial was changed to demonstrate authorization via a group rather than via a direct username.
  • The authorization chapter of the bfg_sql_wiki_tutorial was changed to demonstrate authorization via a group rather than via a direct username.
  • The hooks_chapter chapter now contains a section about changing the request factory.
  • The hooks_chapter chapter now contains sections about changing the request factory and adding a renderer globals factory.
  • The hybrid_chapter chapter now contains a description of the traverse route argument.
  • The API documentation includes a new module: repoze.bfg.renderers.
  • The templates chapter was updated; all narrative that used templating-specific APIs within examples to perform rendering (such as the repoze.bfg.chameleon_zpt.render_template_to_response method) was changed to use repoze.bfg.renderers render_* functions.
  • Added description of the repoze.bfg.events.subscriber decorator to the events_chapter narrative documentation chapter.
  • Added repoze.bfg.events.subscriber API documentation to repoze.bfg.events API docs.
  • Added a section named "Zope 3 Enforces 'TTW' Authorization Checks By Default; BFG Does Not" to the design_defense chapter.
  • Expanded the cleaning_up_after_a_request section of the URL Dispatch narrative chapter.
  • Expanded the redirecting_to_slash_appended_routes section of the URL Dispatch narrative chapter.

Licensing Changes

  • The Edgewall (BSD) license was added to the LICENSES.txt file, as some code in the repoze.bfg.i18n module derives from Babel source.