Here's some sci fi I wrote up about a "page" ZCML directive. As Tim Hoffman
suggested, maybe the fact that the "page" is passed into the template would
give us enough "pull" capability to avoid any of the other hacks I proposed to
push global names into every rendered template.
Note that the "view" directive could probably eventually be changed to do
everything that the "page" directive I describe below does.
``repoze.bfg.page`` is a package which adds a ``page`` ZCML directive
to the set of directives that may be used under BFG. You might use a
``page`` directive in places where you would otherwise use the
built-in repoze.bfg ``view`` directive. Defining a ``page`` directive
effectively creates a single BFG view "under the hood", and owns
attributes similar to those of a view directive. However, the
``page`` directive differs from the BFG ``view`` directive in a number
of important ways:
- The ``page`` directive allows you to associate a *template* with the
page being defined. The machinery behind the ``page`` directive is
capable of rendering an associated template, unlike a view, which
must find and render a template itself.
- A ``page`` directive, like a BFG ``view`` directive, points at a
callable which accepts two arguments: ``context`` and ``request``.
This callable must return a Response object *or* a Python
dictionary. This is unlike a BFG ``view`` callable, which always
returns a Response object (and must never return a dictionary).
The ``callable`` which a ``page`` directive points at may optionally
be a class. If the page directive's ``callable`` attribute points
at a class, that class must have an ``__init__`` method that accepts
two arguments: ``context`` and ``request``. That class must further
define a ``__call__`` method which accepts no arguments and which
returns a dictionary or a Response object.
If the page callable returns a Python dictionary, the ``template``
named within the directive will be passed the dictionary as its
keyword arguments, and the ``page`` implementation will return the
resulting rendered template in a response to the user. The callable
object (whatever object was used to define the page ``callable``)
will be automatically inserted into the set of keyword arguments
passed to the template as ``page``. If the callable object was a
class, an instance of that class will be inserted into the keyword
arguments as ``page``.
If the ``callable`` associated with a ``page`` directive returns a
Response object (an object with the attributes ``status``,
``headerlist`` and ``app_iter``), any template associated with the
``page`` declaration is ignored, and the response is passed back to
BFG. For example, if your page callable returns an ``HTTPFound``
response, no template rendering will be performed::
from webob.exc import HTTPFound
return HTTPFound(location='http://example.com') # templating avoided
Here's an example of a page directive which acts as a default view::
The ``template`` attribute is optional. If one is not named, and the
callable returns a dictionary, an error will be thrown at rendering
Special ZCML Attributes
The directive accepts attributes other than ``template`` and ``callable``.
``repoze.bfg.page`` defaults to using the ``__call__`` method of the
page callable to obtain a response dictionary. The ``attr`` value
allows you to vary that method name. For example, if your class had
a method named ``index`` and you wanted to use this method instead
of ``__call__``, you'd say ``attr="index"`` in the page ZCML
definition. This is most useful when the page definition is a
A Python dotted-path name representing the Python class that the
:term:`context` must be an instance of, *or* the :term:`interface`
that the :term:`context` must provide in order for this view to be
found and called.
The *view name*. Read and understand :ref:`traversal_chapter` to
understand the concept of a view name.
The name of a *permission* that the user must possess in order to
call the view. See :ref:`view_security_section` for more
information about view security and permissions.
This value can either be one of the strings 'GET', 'POST', 'PUT',
'DELETE', or 'HEAD' representing an HTTP ``REQUEST_METHOD``. A view
declaration with this attribute ensures that the view will only be
called when the request's ``method`` (aka ``REQUEST_METHOD``) string
matches the supplied value.
This value can be any string. A view declaration with this
attribute ensures that the view will only be called when the request
has a key in the ``request.params`` dictionary (an HTTP ``GET`` or
``POST`` variable) that has a name which matches the supplied value.
If the value supplied to the attribute has a ``=`` sign in it,
e.g. ``request_params="foo=123"``, then the key (``foo``) must both
exist in the ``request.params`` dictionary, and the value must match
the right hand side of the expression (``123``) for the view to
"match" the current request.
This value should be a Python dotted-path string representing the
class that a graph traversal parent object of the :term:`context`
must be an instance of (or :term:`interface` that a parent object
must provide) in order for this view to be found and called. Your
models must be "location-aware" to use this feature. See
:ref:`location_aware` for more information about location-awareness.
*This attribute services an advanced feature that isn't often used
unless you want to perform traversal *after* a route has matched.*
This value must match the ``name`` of a ``<route>`` declaration (see
:ref:`urldispatch_chapter`) that must match before this view will be
called. The ``<route>`` declaration specified by ``route_name`` must
exist in ZCML before the view that names the route
(XML-ordering-wise) . Note that the ``<route>`` declaration
referred to by ``route_name`` usually has a ``*traverse`` token in
the value of its ``path`` attribute, representing a part of the path
that will be used by traversal against the result of the route's
:term:`root factory`. See :ref:`hybrid_chapter` for more
information on using this advanced feature.
This value should be a Python dotted-path string representing the
:term:`interface` that the :term:`request` must have in order for
this view to be found and called. See
:ref:`view_request_types_section` for more information about request
types. For backwards compatibility with :mod:`repoze.bfg` version
1.0, this value may also be an HTTP ``REQUEST_METHOD`` string, e.g.
('GET', 'HEAD', 'PUT', 'POST', or 'DELETE'). Passing request method
strings as a ``request_type`` is deprecated. Use the
``request_method`` attribute instead for maximum forward
Special Keyword Names When A Callable Returns A Dictionary
Several keyword names in a dictionary return value of a page callable
are treated specially by the page implementation. These values are
passed through to the template during rendering, but they also
influence the response returned to the user separate from any template
rendering. Page callables should set these values into the dictionary
they return to influence response attributes.
Defines the content-type of the resulting response,
A sequence of tuples describing cookie values that should be set in
the response, e.g. ``[('Set-Cookie', 'abc=123'), ('X-My-Header',
A WSGI-style status code (e.g. ``200 OK``) describing the status of
The character set (e.g. ``UTF-8``) of the response.
A value in seconds which will influence ``Cache-Control`` and
``Expires`` headers in the returned response. The same can also be
achieved by returning various values in the headerlist, this is
purely a convenience.
Default Template Filename Extension Mappings
A file extension mapping is used to determine which templating system
renderer to use to render any given template. By default, a single
filename-extension-to-renderer mapping is used: any template name with
a filename extension of ".pt" is assumed to be rendered via a
Chameleon ZPT template.
By default, if a template renderer cannot be recognized by its
extension, it will be assumed that a Chameleon text renderer should be
used to render the template.
Adding and Overriding Template Filename Extension Mappings
Additonal declarations can be made which override a default
file-extension-to-renderer mapping or add a new
file-extension-to-renderer mapping. This is accomplished via one or
more separate ZCML directives.
For example, to add Jinja2 rendering (after installing the
repoze.bfg.jinja2" package), whereby filenames that end in ``.jinja``
are rendered by the Jinja2 renderer::
To override the default mapping in which files with a ``.pt``
extension are rendered via a Chameleon ZPT page template renderer, use
a variation on the following::
By default, when a template extension is unrecognized, the Chameleon
text templating engine is assumed. You can override the default
renderer by creating an ``IPageRenderer`` utility which has no
The ``component`` named within any of these directives must be a
callable which accepts the following arguments: ``(template_name,
request, **kw)``. It must return a Response object.
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