What's New in Pyramid 1.1

This article explains the new features in Pyramid version 1.1 as compared to its predecessor, Pyramid 1.0. It also documents backwards incompatibilities between the two versions and deprecations added to Pyramid 1.1, as well as software dependency changes and notable documentation additions.

Terminology Changes

The term "template" used by the Pyramid documentation used to refer to both "paster templates" and "rendered templates" (templates created by a rendering engine. i.e. Mako, Chameleon, Jinja, etc.). "Paster templates" will now be referred to as "scaffolds", whereas the name for "rendered templates" will remain as "templates."

Major Feature Additions

The major feature additions in Pyramid 1.1 are:

  • Support for the request.response attribute.

  • New views introspection feature: paster pviews.

  • Support for "static" routes.

  • Default HTTP exception view.

  • http_cache view configuration parameter causes Pyramid to set HTTP caching headers.

  • Features that make it easier to write scripts that work in a Pyramid environment.

request.response

  • Instances of the pyramid.request.Request class now have a response attribute.

    The object passed to a view callable as request is an instance of pyramid.request.Request. request.response is an instance of the class pyramid.response.Response. View callables that are configured with a renderer will return this response object to the Pyramid router. Therefore, code in a renderer-using view callable can set response attributes such as request.response.content_type (before they return, e.g. a dictionary to the renderer) and this will influence the HTTP return value of the view callable.

    request.response can also be used in view callable code that is not configured to use a renderer. For example, a view callable might do request.response.body = '123'; return request.response. However, the response object that is produced by request.response must be returned when a renderer is not in play in order to have any effect on the HTTP response (it is not a "global" response, and modifications to it are not somehow merged into a separately returned response object).

    The request.response object is lazily created, so its introduction does not negatively impact performance.

paster pviews

Static Routes

  • The add_route method of the Configurator now accepts a static argument. If this argument is True, the added route will never be considered for matching when a request is handled. Instead, it will only be useful for URL generation via route_url and route_path. See the section entitled Static Routes for more information.

Default HTTP Exception View

  • A default exception view for the interface pyramid.interfaces.IExceptionResponse is now registered by default. This means that an instance of any exception class imported from pyramid.httpexceptions (such as HTTPFound) can now be raised from within view code; when raised, this exception view will render the exception to a response.

    To allow for configuration of this feature, the Configurator now accepts an additional keyword argument named exceptionresponse_view. By default, this argument is populated with a default exception view function that will be used when an HTTP exception is raised. When None is passed for this value, an exception view for HTTP exceptions will not be registered. Passing None returns the behavior of raising an HTTP exception to that of Pyramid 1.0 (the exception will propagate to middleware and to the WSGI server).

http_cache

A new value http_cache can be used as a view configuration parameter.

When you supply an http_cache value to a view configuration, the Expires and Cache-Control headers of a response generated by the associated view callable are modified. The value for http_cache may be one of the following:

  • A nonzero integer. If it's a nonzero integer, it's treated as a number of seconds. This number of seconds will be used to compute the Expires header and the Cache-Control: max-age parameter of responses to requests which call this view. For example: http_cache=3600 instructs the requesting browser to 'cache this response for an hour, please'.

  • A datetime.timedelta instance. If it's a datetime.timedelta instance, it will be converted into a number of seconds, and that number of seconds will be used to compute the Expires header and the Cache-Control: max-age parameter of responses to requests which call this view. For example: http_cache=datetime.timedelta(days=1) instructs the requesting browser to 'cache this response for a day, please'.

  • Zero (0). If the value is zero, the Cache-Control and Expires headers present in all responses from this view will be composed such that client browser cache (and any intermediate caches) are instructed to never cache the response.

  • A two-tuple. If it's a two tuple (e.g. http_cache=(1, {'public':True})), the first value in the tuple may be a nonzero integer or a datetime.timedelta instance; in either case this value will be used as the number of seconds to cache the response. The second value in the tuple must be a dictionary. The values present in the dictionary will be used as input to the Cache-Control response header. For example: http_cache=(3600, {'public':True}) means 'cache for an hour, and add public to the Cache-Control header of the response'. All keys and values supported by the webob.cachecontrol.CacheControl interface may be added to the dictionary. Supplying {'public':True} is equivalent to calling response.cache_control.public = True.

Providing a non-tuple value as http_cache is equivalent to calling response.cache_expires(value) within your view's body.

Providing a two-tuple value as http_cache is equivalent to calling response.cache_expires(value[0], **value[1]) within your view's body.

If you wish to avoid influencing, the Expires header, and instead wish to only influence Cache-Control headers, pass a tuple as http_cache with the first element of None, e.g.: (None, {'public':True}).

The environment setting PYRAMID_PREVENT_HTTP_CACHE and configuration file value prevent_http_cache are synonymous and allow you to prevent HTTP cache headers from being set by Pyramid's http_cache machinery globally in a process. see Influencing HTTP Caching and Preventing HTTP Caching.

Easier Scripting Writing

A new API function pyramid.paster.bootstrap() has been added to make writing scripts that need to work under Pyramid environment easier, e.g.:

from pyramid.paster import bootstrap
info = bootstrap('/path/to/my/development.ini')
request = info['request']
print request.route_url('myroute')

See Writing a Script for more details.

Minor Feature Additions

  • It is now possible to invoke paster pshell even if the paste ini file section name pointed to in its argument is not actually a Pyramid WSGI application. The shell will work in a degraded mode, and will warn the user. See "The Interactive Shell" in the "Creating a Pyramid Project" narrative documentation section.

  • The paster pshell, paster pviews, and paster proutes commands each now under the hood uses pyramid.paster.bootstrap(), which makes it possible to supply an .ini file without naming the "right" section in the file that points at the actual Pyramid application. Instead, you can generally just run paster {pshell|proutes|pviews} development.ini and it will do mostly the right thing.

  • It is now possible to add a [pshell] section to your application's .ini configuration file, which influences the global names available to a pshell session. See Extending the Shell.

  • The pyramid.config.Configurator.scan() method has grown a **kw argument. kw argument represents a set of keyword arguments to pass to the Venusian Scanner object created by Pyramid. (See the Venusian documentation for more information about Scanner).

  • New request property: json_body. This property will return the JSON-decoded variant of the request body. If the request body is not well-formed JSON, this property will raise an exception.

  • A JSONP renderer. See JSONP Renderer for more details.

  • New authentication policy: pyramid.authentication.SessionAuthenticationPolicy, which uses a session to store credentials.

  • A function named pyramid.httpexceptions.exception_response() is a shortcut that can be used to create HTTP exception response objects using an HTTP integer status code.

  • Integers and longs passed as elements to pyramid.url.resource_url() or pyramid.request.Request.resource_url() e.g. resource_url(context, request, 1, 2) (1 and 2 are the elements) will now be converted implicitly to strings in the result. Previously passing integers or longs as elements would cause a TypeError.

  • pyramid_alchemy scaffold now uses query.get rather than query.filter_by to take better advantage of identity map caching.

  • pyramid_alchemy scaffold now has unit tests.

  • Added a pyramid.i18n.make_localizer() API.

  • An exception raised by a pyramid.events.NewRequest event subscriber can now be caught by an exception view.

  • It is now possible to get information about why Pyramid raised a Forbidden exception from within an exception view. The ACLDenied object returned by the permits method of each stock authorization policy (pyramid.interfaces.IAuthorizationPolicy.permits()) is now attached to the Forbidden exception as its result attribute. Therefore, if you've created a Forbidden exception view, you can see the ACE, ACL, permission, and principals involved in the request as eg. context.result.permission, context.result.acl, etc within the logic of the Forbidden exception view.

  • Don't explicitly prevent the timeout from being lower than the reissue_time when setting up an pyramid.authentication.AuthTktAuthenticationPolicy (previously such a configuration would raise a ValueError, now it's allowed, although typically nonsensical). Allowing the nonsensical configuration made the code more understandable and required fewer tests.

  • The pyramid.request.Request class now has a ResponseClass attribute which points at pyramid.response.Response.

  • The pyramid.response.Response class now has a RequestClass interface which points at pyramid.request.Request.

  • It is now possible to return an arbitrary object from a Pyramid view callable even if a renderer is not used, as long as a suitable adapter to pyramid.interfaces.IResponse is registered for the type of the returned object by using the new pyramid.config.Configurator.add_response_adapter() API. See the section in the Hooks chapter of the documentation entitled Changing How Pyramid Treats View Responses.

  • The Pyramid router will now, by default, call the __call__ method of response objects when returning a WSGI response. This means that, among other things, the conditional_response feature response objects inherited from WebOb will now behave properly.

  • New method named pyramid.request.Request.is_response(). This method should be used instead of the pyramid.view.is_response() function, which has been deprecated.

  • pyramid.exceptions.NotFound is now just an alias for pyramid.httpexceptions.HTTPNotFound.

  • pyramid.exceptions.Forbidden is now just an alias for pyramid.httpexceptions.HTTPForbidden.

  • Added mako.preprocessor config file parameter; allows for a Mako preprocessor to be specified as a Python callable or Python dotted name. See https://github.com/Pylons/pyramid/pull/183 for rationale.

  • New API class: pyramid.static.static_view. This supersedes the (now deprecated) pyramid.view.static class. pyramid.static.static_view, by default, serves up documents as the result of the request's path_info, attribute rather than it's subpath attribute (the inverse was true of pyramid.view.static, and still is). pyramid.static.static_view exposes a use_subpath flag for use when you want the static view to behave like the older deprecated version.

  • A new api function pyramid.scripting.prepare() has been added. It is a lower-level analogue of pyramid.paster.bootstrap() that accepts a request and a registry instead of a config file argument, and is used for the same purpose:

    from pyramid.scripting import prepare
info = prepare(registry=myregistry)
request = info['request']
print request.route_url('myroute')

  • A new API function pyramid.scripting.make_request() has been added. The resulting request will have a registry attribute. It is meant to be used in conjunction with pyramid.scripting.prepare() and/or pyramid.paster.bootstrap() (both of which accept a request as an argument):

    from pyramid.scripting import make_request
request = make_request('/')

  • New API attribute pyramid.config.global_registries is an iterable object that contains references to every Pyramid registry loaded into the current process via pyramid.config.Configurator.make_wsgi_app(). It also has a last attribute containing the last registry loaded. This is used by the scripting machinery, and is available for introspection.

  • Added the pyramid.renderers.null_renderer object as an API. The null renderer is an object that can be used in advanced integration cases as input to the view configuration renderer= argument. When the null renderer is used as a view renderer argument, Pyramid avoids converting the view callable result into a Response object. This is useful if you want to reuse the view configuration and lookup machinery outside the context of its use by the Pyramid router. (This feature was added for consumption by the pyramid_rpc package, which uses view configuration and lookup outside the context of a router in exactly this way.)

Backwards Incompatibilities

  • Pyramid no longer supports Python 2.4. Python 2.5 or better is required to run Pyramid 1.1+. Pyramid, however, does not work under any version of Python 3 yet.

  • The Pyramid router now, by default, expects response objects returned from view callables to implement the pyramid.interfaces.IResponse interface. Unlike the Pyramid 1.0 version of this interface, objects which implement IResponse now must define a __call__ method that accepts environ and start_response, and which returns an app_iter iterable, among other things. Previously, it was possible to return any object which had the three WebOb app_iter, headerlist, and status attributes as a response, so this is a backwards incompatibility. It is possible to get backwards compatibility back by registering an adapter to IResponse from the type of object you're now returning from view callables. See the section in the Hooks chapter of the documentation entitled Changing How Pyramid Treats View Responses.

  • The pyramid.interfaces.IResponse interface is now much more extensive. Previously it defined only app_iter, status and headerlist; now it is basically intended to directly mirror the webob.Response API, which has many methods and attributes.

  • The pyramid.httpexceptions classes named HTTPFound, HTTPMultipleChoices, HTTPMovedPermanently, HTTPSeeOther, HTTPUseProxy, and HTTPTemporaryRedirect now accept location as their first positional argument rather than detail. This means that you can do, e.g. return pyramid.httpexceptions.HTTPFound('http://foo') rather than return pyramid.httpexceptions.HTTPFound(location='http//foo') (the latter will of course continue to work).

  • The pyramid Router attempted to set a value into the key environ['repoze.bfg.message'] when it caught a view-related exception for backwards compatibility with applications written for repoze.bfg during error handling. It did this by using code that looked like so:

    # "why" is an exception object
try:
    msg = why[0]
except:
    msg = ''

environ['repoze.bfg.message'] = msg

    Use of the value environ['repoze.bfg.message'] was docs-deprecated in Pyramid 1.0. Our standing policy is to not remove features after a deprecation for two full major releases, so this code was originally slated to be removed in Pyramid 1.2. However, computing the repoze.bfg.message value was the source of at least one bug found in the wild (https://github.com/Pylons/pyramid/issues/199), and there isn't a foolproof way to both preserve backwards compatibility and to fix the bug. Therefore, the code which sets the value has been removed in this release. Code in exception views which relies on this value's presence in the environment should now use the exception attribute of the request (e.g. request.exception[0]) to retrieve the message instead of relying on request.environ['repoze.bfg.message'].

Deprecations and Behavior Differences

Note

Under Python 2.7+, it's necessary to pass the Python interpreter the correct warning flags to see deprecation warnings emitted by Pyramid when porting your application from an older version of Pyramid. Use the PYTHONWARNINGS environment variable with the value all in the shell you use to invoke paster serve to see these warnings, e.g. on Unix, PYTHONWARNINGS=all $VENV/bin/paster serve development.ini. Python 2.5 and 2.6 show deprecation warnings by default, so this is unnecessary there. All deprecation warnings are emitted to the console.

  • The pyramid.view.static class has been deprecated in favor of the newer pyramid.static.static_view class. A deprecation warning is raised when it is used. You should replace it with a reference to pyramid.static.static_view with the use_subpath=True argument.

  • The paster pshell, paster proutes, and paster pviews commands now take a single argument in the form /path/to/config.ini#sectionname rather than the previous 2-argument spelling /path/to/config.ini sectionname. #sectionname may be omitted, in which case #main is assumed.

  • The default Mako renderer is now configured to escape all HTML in expression tags. This is intended to help prevent XSS attacks caused by rendering unsanitized input from users. To revert this behavior in user's templates, they need to filter the expression through the 'n' filter:

    ${ myhtml | n }.

    See https://github.com/Pylons/pyramid/issues/193.

  • Deprecated all assignments to request.response_* attributes (for example request.response_content_type = 'foo' is now deprecated). Assignments and mutations of assignable request attributes that were considered by the framework for response influence are now deprecated: response_content_type, response_headerlist, response_status, response_charset, and response_cache_for. Instead of assigning these to the request object for later detection by the rendering machinery, users should use the appropriate API of the Response object created by accessing request.response (e.g. code which does request.response_content_type = 'abc' should be changed to request.response.content_type = 'abc').

  • Passing view-related parameters to pyramid.config.Configurator.add_route() is now deprecated. Previously, a view was permitted to be connected to a route using a set of view* parameters passed to the add_route method of the Configurator. This was a shorthand which replaced the need to perform a subsequent call to add_view. For example, it was valid (and often recommended) to do:

    config.add_route('home', '/', view='mypackage.views.myview',
                  view_renderer='some/renderer.pt')

    Passing view* arguments to add_route is now deprecated in favor of connecting a view to a predefined route via pyramid.config.Configurator.add_view() using the route's route_name parameter. As a result, the above example should now be spelled:

    config.add_route('home', '/')
config.add_view('mypackage.views.myview', route_name='home',
                renderer='some/renderer.pt')

    This deprecation was done to reduce confusion observed in IRC, as well as to (eventually) reduce documentation burden. A deprecation warning is now issued when any view-related parameter is passed to add_route.

    See also

    See also issue #164 on GitHub.

  • Passing an environ dictionary to the __call__ method of a "traverser" (e.g. an object that implements pyramid.interfaces.ITraverser such as an instance of pyramid.traversal.ResourceTreeTraverser) as its request argument now causes a deprecation warning to be emitted. Consumer code should pass a request object instead. The fact that passing an environ dict is permitted has been documentation-deprecated since repoze.bfg 1.1, and this capability will be removed entirely in a future version.

  • The following (undocumented, dictionary-like) methods of the pyramid.request.Request object have been deprecated: __contains__, __delitem__, __getitem__, __iter__, __setitem__, get, has_key, items, iteritems, itervalues, keys, pop, popitem, setdefault, update, and values. Usage of any of these methods will cause a deprecation warning to be emitted. These methods were added for internal compatibility in repoze.bfg 1.1 (code that currently expects a request object expected an environ object in BFG 1.0 and before). In a future version, these methods will be removed entirely.

  • A custom request factory is now required to return a request object that has a response attribute (or "reified"/lazy property) if the request is meant to be used in a view that uses a renderer. This response attribute should be an instance of the class pyramid.response.Response.

  • The JSON and string renderer factories now assign to request.response.content_type rather than request.response_content_type.

  • Each built-in renderer factory now determines whether it should change the content type of the response by comparing the response's content type against the response's default content type; if the content type is the default content type (usually text/html), the renderer changes the content type (to application/json or text/plain for JSON and string renderers respectively).

  • The pyramid.wsgi.wsgiapp2() now uses a slightly different method of figuring out how to "fix" SCRIPT_NAME and PATH_INFO for the downstream application. As a result, those values may differ slightly from the perspective of the downstream application (for example, SCRIPT_NAME will now never possess a trailing slash).

  • Previously, pyramid.request.Request inherited from webob.request.Request and implemented __getattr__, __setattr__ and __delattr__ itself in order to override "adhoc attr" WebOb behavior where attributes of the request are stored in the environ. Now, pyramid.request.Request inherits from (the more recent) webob.request.BaseRequest instead of webob.request.Request, which provides the same behavior. pyramid.request.Request no longer implements its own __getattr__, __setattr__ or __delattr__ as a result.

  • Deprecated pyramid.view.is_response() function in favor of (newly-added) pyramid.request.Request.is_response() method. Determining if an object is truly a valid response object now requires access to the registry, which is only easily available as a request attribute. The pyramid.view.is_response() function will still work until it is removed, but now may return an incorrect answer under some (very uncommon) circumstances.

  • pyramid.response.Response is now a subclass of webob.response.Response (in order to directly implement the pyramid.interfaces.IResponse interface, to speed up response generation).

  • The "exception response" objects importable from pyramid.httpexceptions (e.g. HTTPNotFound) are no longer just import aliases for classes that actually live in webob.exc. Instead, we've defined our own exception classes within the module that mirror and emulate the webob.exc exception response objects almost entirely. See Pyramid uses its own HTTP exception class hierarchy rather than webob.exc in the Design Defense chapter for more information.

  • When visiting a URL that represented a static view which resolved to a subdirectory, the index.html of that subdirectory would not be served properly. Instead, a redirect to /subdir would be issued. This has been fixed, and now visiting a subdirectory that contains an index.html within a static view returns the index.html properly.

    See also

    See also issue #67 on GitHub.

  • Deprecated the pyramid.config.Configurator.set_renderer_globals_factory method and the renderer_globals Configurator constructor parameter. Users should convert code using this feature to use a BeforeRender event. See the section Using the Before Render Event in the Hooks chapter.

  • In Pyramid 1.0, the pyramid.events.subscriber directive behaved contrary to the documentation when passed more than one interface object to its constructor. For example, when the following listener was registered:

    @subscriber(IFoo, IBar)
def expects_ifoo_events_and_ibar_events(event):
    print event

    The Events chapter docs claimed that the listener would be registered and listening for both IFoo and IBar events. Instead, it registered an "object event" subscriber which would only be called if an IObjectEvent was emitted where the object interface was IFoo and the event interface was IBar.

    The behavior now matches the documentation. If you were relying on the buggy behavior of the 1.0 subscriber directive in order to register an object event subscriber, you must now pass a sequence to indicate you'd like to register a subscriber for an object event. e.g.:

    @subscriber([IFoo, IBar])
def expects_object_event(object, event):
    print object, event

  • In 1.0, if a pyramid.events.BeforeRender event subscriber added a value via the __setitem__ or update methods of the event object with a key that already existed in the renderer globals dictionary, a KeyError was raised. With the deprecation of the "add_renderer_globals" feature of the configurator, there was no way to override an existing value in the renderer globals dictionary that already existed. Now, the event object will overwrite an older value that is already in the globals dictionary when its __setitem__ or update is called (as well as the new setdefault method), just like a plain old dictionary. As a result, for maximum interoperability with other third-party subscribers, if you write an event subscriber meant to be used as a BeforeRender subscriber, your subscriber code will now need to (using .get or __contains__ of the event object) ensure no value already exists in the renderer globals dictionary before setting an overriding value.

  • The pyramid.config.Configurator.add_route() method allowed two routes with the same route to be added without an intermediate call to pyramid.config.Configurator.commit(). If you now receive a ConfigurationError at startup time that appears to be add_route related, you'll need to either a) ensure that all of your route names are unique or b) call config.commit() before adding a second route with the name of a previously added name or c) use a Configurator that works in autocommit mode.

Dependency Changes

  • Pyramid now depends on WebOb >= 1.0.2 as tests depend on the bugfix in that release: "Fix handling of WSGI environs with missing SCRIPT_NAME". (Note that in reality, everyone should probably be using 1.0.4 or better though, as WebOb 1.0.2 and 1.0.3 were effectively brownbag releases.)

Documentation Enhancements