diff options
| -rw-r--r-- | docs/narr/traversal.rst | 425 |
1 files changed, 204 insertions, 221 deletions
diff --git a/docs/narr/traversal.rst b/docs/narr/traversal.rst index 454bb5620..cd8395eac 100644 --- a/docs/narr/traversal.rst +++ b/docs/narr/traversal.rst @@ -3,32 +3,30 @@ Traversal ========= -This chapter explains the technical details of how traversal works in -Pyramid. +This chapter explains the technical details of how traversal works in Pyramid. For a quick example, see :doc:`hellotraversal`. For more about *why* you might use traversal, see :doc:`muchadoabouttraversal`. A :term:`traversal` uses the URL (Universal Resource Locator) to find a -:term:`resource` located in a :term:`resource tree`, which is a set of -nested dictionary-like objects. Traversal is done by using each segment -of the path portion of the URL to navigate through the :term:`resource -tree`. You might think of this as looking up files and directories in a -file system. Traversal walks down the path until it finds a published -resource, analogous to a file system "directory" or "file". The -resource found as the result of a traversal becomes the -:term:`context` of the :term:`request`. Then, the :term:`view lookup` -subsystem is used to find some view code willing to "publish" this +:term:`resource` located in a :term:`resource tree`, which is a set of nested +dictionary-like objects. Traversal is done by using each segment of the path +portion of the URL to navigate through the :term:`resource tree`. You might +think of this as looking up files and directories in a file system. Traversal +walks down the path until it finds a published resource, analogous to a file +system "directory" or "file". The resource found as the result of a traversal +becomes the :term:`context` of the :term:`request`. Then, the :term:`view +lookup` subsystem is used to find some view code willing to "publish" this resource by generating a :term:`response`. .. note:: Using :term:`Traversal` to map a URL to code is optional. If you're creating - your first Pyramid application it probably makes more sense to use :term:`URL - dispatch` to map URLs to code instead of traversal, as new Pyramid developers - tend to find URL dispatch slightly easier to understand. If you use URL - dispatch, you needn't read this chapter. + your first Pyramid application, it probably makes more sense to use + :term:`URL dispatch` to map URLs to code instead of traversal, as new Pyramid + developers tend to find URL dispatch slightly easier to understand. If you + use URL dispatch, you needn't read this chapter. .. index:: single: traversal details @@ -36,33 +34,32 @@ resource by generating a :term:`response`. Traversal Details ----------------- -:term:`Traversal` is dependent on information in a :term:`request` -object. Every :term:`request` object contains URL path information in -the ``PATH_INFO`` portion of the :term:`WSGI` environment. The -``PATH_INFO`` string is the portion of a request's URL following the -hostname and port number, but before any query string elements or -fragment element. For example the ``PATH_INFO`` portion of the URL -``http://example.com:8080/a/b/c?foo=1`` is ``/a/b/c``. +:term:`Traversal` is dependent on information in a :term:`request` object. +Every :term:`request` object contains URL path information in the ``PATH_INFO`` +portion of the :term:`WSGI` environment. The ``PATH_INFO`` string is the +portion of a request's URL following the hostname and port number, but before +any query string elements or fragment element. For example the ``PATH_INFO`` +portion of the URL ``http://example.com:8080/a/b/c?foo=1`` is ``/a/b/c``. -Traversal treats the ``PATH_INFO`` segment of a URL as a sequence of -path segments. For example, the ``PATH_INFO`` string ``/a/b/c`` is -converted to the sequence ``['a', 'b', 'c']``. +Traversal treats the ``PATH_INFO`` segment of a URL as a sequence of path +segments. For example, the ``PATH_INFO`` string ``/a/b/c`` is converted to the +sequence ``['a', 'b', 'c']``. -This path sequence is then used to descend through the :term:`resource -tree`, looking up a resource for each path segment. Each lookup uses the +This path sequence is then used to descend through the :term:`resource tree`, +looking up a resource for each path segment. Each lookup uses the ``__getitem__`` method of a resource in the tree. For example, if the path info sequence is ``['a', 'b', 'c']``: - :term:`Traversal` starts by acquiring the :term:`root` resource of the - application by calling the :term:`root factory`. The :term:`root factory` - can be configured to return whatever object is appropriate as the - traversal root of your application. + application by calling the :term:`root factory`. The :term:`root factory` can + be configured to return whatever object is appropriate as the traversal root + of your application. -- Next, the first element (``'a'``) is popped from the path segment - sequence and is used as a key to lookup the corresponding resource - in the root. This invokes the root resource's ``__getitem__`` method - using that value (``'a'``) as an argument. +- Next, the first element (``'a'``) is popped from the path segment sequence + and is used as a key to lookup the corresponding resource in the root. This + invokes the root resource's ``__getitem__`` method using that value (``'a'``) + as an argument. - If the root resource "contains" a resource with key ``'a'``, its ``__getitem__`` method will return it. The :term:`context` temporarily @@ -72,29 +69,26 @@ For example, if the path info sequence is ``['a', 'b', 'c']``: resource's ``__getitem__`` is called with that value (``'b'``) as an argument; we'll presume it succeeds. -- The "A" resource's ``__getitem__`` returns another resource, which - we'll call "B". The :term:`context` temporarily becomes the "B" - resource. +- The "A" resource's ``__getitem__`` returns another resource, which we'll call + "B". The :term:`context` temporarily becomes the "B" resource. -Traversal continues until the path segment sequence is exhausted or a -path element cannot be resolved to a resource. In either case, the -:term:`context` resource is the last object that the traversal -successfully resolved. If any resource found during traversal lacks a -``__getitem__`` method, or if its ``__getitem__`` method raises a -:exc:`KeyError`, traversal ends immediately, and that resource becomes -the :term:`context`. +Traversal continues until the path segment sequence is exhausted or a path +element cannot be resolved to a resource. In either case, the :term:`context` +resource is the last object that the traversal successfully resolved. If any +resource found during traversal lacks a ``__getitem__`` method, or if its +``__getitem__`` method raises a :exc:`KeyError`, traversal ends immediately, +and that resource becomes the :term:`context`. The results of a :term:`traversal` also include a :term:`view name`. If -traversal ends before the path segment sequence is exhausted, the -:term:`view name` is the *next* remaining path segment element. If the -:term:`traversal` expends all of the path segments, then the :term:`view -name` is the empty string (``''``). +traversal ends before the path segment sequence is exhausted, the :term:`view +name` is the *next* remaining path segment element. If the :term:`traversal` +expends all of the path segments, then the :term:`view name` is the empty +string (``''``). -The combination of the context resource and the :term:`view name` found -via traversal is used later in the same request by the :term:`view -lookup` subsystem to find a :term:`view callable`. How :app:`Pyramid` -performs view lookup is explained within the :ref:`view_config_chapter` -chapter. +The combination of the context resource and the :term:`view name` found via +traversal is used later in the same request by the :term:`view lookup` +subsystem to find a :term:`view callable`. How :app:`Pyramid` performs view +lookup is explained within the :ref:`view_config_chapter` chapter. .. index:: single: object tree @@ -106,20 +100,20 @@ chapter. The Resource Tree ----------------- -The resource tree is a set of nested dictionary-like resource objects -that begins with a :term:`root` resource. In order to use -:term:`traversal` to resolve URLs to code, your application must supply -a :term:`resource tree` to :app:`Pyramid`. +The resource tree is a set of nested dictionary-like resource objects that +begins with a :term:`root` resource. In order to use :term:`traversal` to +resolve URLs to code, your application must supply a :term:`resource tree` to +:app:`Pyramid`. In order to supply a root resource for an application the :app:`Pyramid` -:term:`Router` is configured with a callback known as a :term:`root -factory`. The root factory is supplied by the application, at startup -time, as the ``root_factory`` argument to the :term:`Configurator`. +:term:`Router` is configured with a callback known as a :term:`root factory`. +The root factory is supplied by the application at startup time as the +``root_factory`` argument to the :term:`Configurator`. -The root factory is a Python callable that accepts a :term:`request` -object, and returns the root object of the :term:`resource tree`. A -function, or class is typically used as an application's root factory. -Here's an example of a simple root factory class: +The root factory is a Python callable that accepts a :term:`request` object, +and returns the root object of the :term:`resource tree`. A function or class +is typically used as an application's root factory. Here's an example of a +simple root factory class: .. code-block:: python :linenos: @@ -136,62 +130,60 @@ passing it to an instance of a :term:`Configurator` named ``config``: config = Configurator(root_factory=Root) -The ``root_factory`` argument to the -:class:`~pyramid.config.Configurator` constructor registers this root -factory to be called to generate a root resource whenever a request -enters the application. The root factory registered this way is also -known as the global root factory. A root factory can alternately be -passed to the ``Configurator`` as a :term:`dotted Python name` which can -refer to a root factory defined in a different module. +The ``root_factory`` argument to the :class:`~pyramid.config.Configurator` +constructor registers this root factory to be called to generate a root +resource whenever a request enters the application. The root factory +registered this way is also known as the global root factory. A root factory +can alternatively be passed to the ``Configurator`` as a :term:`dotted Python +name` which can refer to a root factory defined in a different module. -If no :term:`root factory` is passed to the :app:`Pyramid` -:term:`Configurator` constructor, or if the ``root_factory`` value -specified is ``None``, a :term:`default root factory` is used. The default -root factory always returns a resource that has no child resources; it -is effectively empty. +If no :term:`root factory` is passed to the :app:`Pyramid` :term:`Configurator` +constructor, or if the ``root_factory`` value specified is ``None``, a +:term:`default root factory` is used. The default root factory always returns +a resource that has no child resources; it is effectively empty. Usually a root factory for a traversal-based application will be more -complicated than the above ``Root`` class; in particular it may be associated +complicated than the above ``Root`` class. In particular it may be associated with a database connection or another persistence mechanism. The above ``Root`` class is analogous to the default root factory present in Pyramid. The default root factory is very simple and not very useful. .. note:: - If the items contained within the resource tree are "persistent" (they - have state that lasts longer than the execution of a single process), they - become analogous to the concept of :term:`domain model` objects used by - many other frameworks. + If the items contained within the resource tree are "persistent" (they have + state that lasts longer than the execution of a single process), they become + analogous to the concept of :term:`domain model` objects used by many other + frameworks. -The resource tree consists of *container* resources and *leaf* resources. -There is only one difference between a *container* resource and a *leaf* -resource: *container* resources possess a ``__getitem__`` method (making it +The resource tree consists of *container* resources and *leaf* resources. There +is only one difference between a *container* resource and a *leaf* resource: +*container* resources possess a ``__getitem__`` method (making it "dictionary-like") while *leaf* resources do not. The ``__getitem__`` method was chosen as the signifying difference between the two types of resources because the presence of this method is how Python itself typically determines whether an object is "containerish" or not (dictionary objects are "containerish"). -Each container resource is presumed to be willing to return a child resource -or raise a ``KeyError`` based on a name passed to its ``__getitem__``. +Each container resource is presumed to be willing to return a child resource or +raise a ``KeyError`` based on a name passed to its ``__getitem__``. -Leaf-level instances must not have a ``__getitem__``. If instances that -you'd like to be leaves already happen to have a ``__getitem__`` through some +Leaf-level instances must not have a ``__getitem__``. If instances that you'd +like to be leaves already happen to have a ``__getitem__`` through some historical inequity, you should subclass these resource types and cause their ``__getitem__`` methods to simply raise a ``KeyError``. Or just disuse them and think up another strategy. -Usually, the traversal root is a *container* resource, and as such it -contains other resources. However, it doesn't *need* to be a container. -Your resource tree can be as shallow or as deep as you require. +Usually the traversal root is a *container* resource, and as such it contains +other resources. However, it doesn't *need* to be a container. Your resource +tree can be as shallow or as deep as you require. -In general, the resource tree is traversed beginning at its root resource -using a sequence of path elements described by the ``PATH_INFO`` of the -current request; if there are path segments, the root resource's -``__getitem__`` is called with the next path segment, and it is expected to -return another resource. The resulting resource's ``__getitem__`` is called -with the very next path segment, and it is expected to return another -resource. This happens *ad infinitum* until all path segments are exhausted. +In general, the resource tree is traversed beginning at its root resource using +a sequence of path elements described by the ``PATH_INFO`` of the current +request. If there are path segments, the root resource's ``__getitem__`` is +called with the next path segment, and it is expected to return another +resource. The resulting resource's ``__getitem__`` is called with the very +next path segment, and it is expected to return another resource. This happens +*ad infinitum* until all path segments are exhausted. .. index:: single: traversal algorithm @@ -204,17 +196,17 @@ The Traversal Algorithm This section will attempt to explain the :app:`Pyramid` traversal algorithm. We'll provide a description of the algorithm, a diagram of how the algorithm -works, and some example traversal scenarios that might help you understand -how the algorithm operates against a specific resource tree. +works, and some example traversal scenarios that might help you understand how +the algorithm operates against a specific resource tree. We'll also talk a bit about :term:`view lookup`. The -:ref:`view_config_chapter` chapter discusses :term:`view lookup` in -detail, and it is the canonical source for information about views. -Technically, :term:`view lookup` is a :app:`Pyramid` subsystem that is -separated from traversal entirely. However, we'll describe the -fundamental behavior of view lookup in the examples in the next few -sections to give you an idea of how traversal and view lookup cooperate, -because they are almost always used together. +:ref:`view_config_chapter` chapter discusses :term:`view lookup` in detail, and +it is the canonical source for information about views. Technically, +:term:`view lookup` is a :app:`Pyramid` subsystem that is separated from +traversal entirely. However, we'll describe the fundamental behavior of view +lookup in the examples in the next few sections to give you an idea of how +traversal and view lookup cooperate, because they are almost always used +together. .. index:: single: view name @@ -223,26 +215,24 @@ because they are almost always used together. single: root factory single: default view -A Description of The Traversal Algorithm +A Description of the Traversal Algorithm ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -When a user requests a page from your traversal-powered application, the -system uses this algorithm to find a :term:`context` resource and a -:term:`view name`. +When a user requests a page from your traversal-powered application, the system +uses this algorithm to find a :term:`context` resource and a :term:`view name`. -#. The request for the page is presented to the :app:`Pyramid` - :term:`router` in terms of a standard :term:`WSGI` request, which is - represented by a WSGI environment and a WSGI ``start_response`` callable. +#. The request for the page is presented to the :app:`Pyramid` :term:`router` + in terms of a standard :term:`WSGI` request, which is represented by a WSGI + environment and a WSGI ``start_response`` callable. -#. The router creates a :term:`request` object based on the WSGI - environment. +#. The router creates a :term:`request` object based on the WSGI environment. -#. The :term:`root factory` is called with the :term:`request`. It returns - a :term:`root` resource. +#. The :term:`root factory` is called with the :term:`request`. It returns a + :term:`root` resource. #. The router uses the WSGI environment's ``PATH_INFO`` information to - determine the path segments to traverse. The leading slash is stripped - off ``PATH_INFO``, and the remaining path segments are split on the slash + determine the path segments to traverse. The leading slash is stripped off + ``PATH_INFO``, and the remaining path segments are split on the slash character to form a traversal sequence. The traversal algorithm by default attempts to first URL-unquote and then @@ -252,26 +242,26 @@ system uses this algorithm to find a :term:`context` resource and a Conversion from a URL-decoded string into Unicode is attempted using the UTF-8 encoding. If any URL-unquoted path segment in ``PATH_INFO`` is not decodeable using the UTF-8 decoding, a :exc:`TypeError` is raised. A - segment will be fully URL-unquoted and UTF8-decoded before it is passed - in to the ``__getitem__`` of any resource during traversal. + segment will be fully URL-unquoted and UTF8-decoded before it is passed in + to the ``__getitem__`` of any resource during traversal. - Thus, a request with a ``PATH_INFO`` variable of ``/a/b/c`` maps to the + Thus a request with a ``PATH_INFO`` variable of ``/a/b/c`` maps to the traversal sequence ``[u'a', u'b', u'c']``. -#. :term:`Traversal` begins at the root resource returned by the root - factory. For the traversal sequence ``[u'a', u'b', u'c']``, the root - resource's ``__getitem__`` is called with the name ``'a'``. Traversal - continues through the sequence. In our example, if the root resource's - ``__getitem__`` called with the name ``a`` returns a resource (aka +#. :term:`Traversal` begins at the root resource returned by the root factory. + For the traversal sequence ``[u'a', u'b', u'c']``, the root resource's + ``__getitem__`` is called with the name ``'a'``. Traversal continues + through the sequence. In our example, if the root resource's + ``__getitem__`` called with the name ``a`` returns a resource (a.k.a. resource "A"), that resource's ``__getitem__`` is called with the name ``'b'``. If resource "A" returns a resource "B" when asked for ``'b'``, resource B's ``__getitem__`` is then asked for the name ``'c'``, and may return resource "C". -#. Traversal ends when a) the entire path is exhausted or b) when any - resource raises a :exc:`KeyError` from its ``__getitem__`` or c) when any +#. Traversal ends when either (a) the entire path is exhausted, (b) when any + resource raises a :exc:`KeyError` from its ``__getitem__``, (c) when any non-final path element traversal does not have a ``__getitem__`` method - (resulting in a :exc:`AttributeError`) or d) when any path element is + (resulting in an :exc:`AttributeError`), or (d) when any path element is prefixed with the set of characters ``@@`` (indicating that the characters following the ``@@`` token should be treated as a :term:`view name`). @@ -279,13 +269,13 @@ system uses this algorithm to find a :term:`context` resource and a resource found during traversal is deemed to be the :term:`context`. If the path has been exhausted when traversal ends, the :term:`view name` is deemed to be the empty string (``''``). However, if the path was *not* - exhausted before traversal terminated, the first remaining path segment - is treated as the view name. + exhausted before traversal terminated, the first remaining path segment is + treated as the view name. #. Any subsequent path elements after the :term:`view name` is found are deemed the :term:`subpath`. The subpath is always a sequence of path - segments that come from ``PATH_INFO`` that are "left over" after - traversal has completed. + segments that come from ``PATH_INFO`` that are "left over" after traversal + has completed. Once the :term:`context` resource, the :term:`view name`, and associated attributes such as the :term:`subpath` are located, the job of @@ -297,20 +287,19 @@ The traversal algorithm exposes two special cases: - You will often end up with a :term:`view name` that is the empty string as the result of a particular traversal. This indicates that the view lookup - machinery should look up the :term:`default view`. The default view is a - view that is registered with no name or a view which is registered with a - name that equals the empty string. + machinery should lookup the :term:`default view`. The default view is a view + that is registered with no name or a view which is registered with a name + that equals the empty string. -- If any path segment element begins with the special characters ``@@`` - (think of them as goggles), the value of that segment minus the goggle - characters is considered the :term:`view name` immediately and traversal - stops there. This allows you to address views that may have the same names - as resource names in the tree unambiguously. +- If any path segment element begins with the special characters ``@@`` (think + of them as goggles), the value of that segment minus the goggle characters is + considered the :term:`view name` immediately and traversal stops there. This + allows you to address views that may have the same names as resource names in + the tree unambiguously. Finally, traversal is responsible for locating a :term:`virtual root`. A -virtual root is used during "virtual hosting"; see the -:ref:`vhosting_chapter` chapter for information. We won't speak more about -it in this chapter. +virtual root is used during "virtual hosting". See the :ref:`vhosting_chapter` +chapter for information. We won't speak more about it in this chapter. .. image:: resourcetreetraverser.png @@ -321,13 +310,13 @@ Traversal Algorithm Examples ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ No one can be expected to understand the traversal algorithm by analogy and -description alone, so let's examine some traversal scenarios that use -concrete URLs and resource tree compositions. +description alone, so let's examine some traversal scenarios that use concrete +URLs and resource tree compositions. -Let's pretend the user asks for -``http://example.com/foo/bar/baz/biz/buz.txt``. The request's ``PATH_INFO`` -in that case is ``/foo/bar/baz/biz/buz.txt``. Let's further pretend that -when this request comes in that we're traversing the following resource tree: +Let's pretend the user asks for ``http://example.com/foo/bar/baz/biz/buz.txt``. +The request's ``PATH_INFO`` in that case is ``/foo/bar/baz/biz/buz.txt``. +Let's further pretend that when this request comes in, we're traversing the +following resource tree: .. code-block:: text @@ -346,33 +335,32 @@ Here's what happens: finds. - :term:`traversal` traverses "bar", and attempts to find "baz", which it does - not find (the "bar" resource raises a :exc:`KeyError` when asked for - "baz"). + not find (the "bar" resource raises a :exc:`KeyError` when asked for "baz"). The fact that it does not find "baz" at this point does not signify an error -condition. It signifies that: +condition. It signifies the following: -- the :term:`context` is the "bar" resource (the context is the last resource +- The :term:`context` is the "bar" resource (the context is the last resource found during traversal). -- the :term:`view name` is ``baz`` +- The :term:`view name` is ``baz``. -- the :term:`subpath` is ``('biz', 'buz.txt')`` +- The :term:`subpath` is ``('biz', 'buz.txt')``. At this point, traversal has ended, and :term:`view lookup` begins. Because it's the "context" resource, the view lookup machinery examines "bar" -to find out what "type" it is. Let's say it finds that the context is a -``Bar`` type (because "bar" happens to be an instance of the class ``Bar``). -Using the :term:`view name` (``baz``) and the type, view lookup asks the +to find out what "type" it is. Let's say it finds that the context is a ``Bar`` +type (because "bar" happens to be an instance of the class ``Bar``). Using the +:term:`view name` (``baz``) and the type, view lookup asks the :term:`application registry` this question: - Please find me a :term:`view callable` registered using a :term:`view configuration` with the name "baz" that can be used for the class ``Bar``. -Let's say that view lookup finds no matching view type. In this -circumstance, the :app:`Pyramid` :term:`router` returns the result of the -:term:`Not Found View` and the request ends. +Let's say that view lookup finds no matching view type. In this circumstance, +the :app:`Pyramid` :term:`router` returns the result of the :term:`Not Found +View` and the request ends. However, for this tree: @@ -399,59 +387,58 @@ The user asks for ``http://example.com/foo/bar/baz/biz/buz.txt`` - :term:`traversal` traverses "baz", and attempts to find "biz", which it finds. -- :term:`traversal` traverses "biz", and attempts to find "buz.txt" which it +- :term:`traversal` traverses "biz", and attempts to find "buz.txt", which it does not find. The fact that it does not find a resource related to "buz.txt" at this point -does not signify an error condition. It signifies that: +does not signify an error condition. It signifies the following: -- the :term:`context` is the "biz" resource (the context is the last resource +- The :term:`context` is the "biz" resource (the context is the last resource found during traversal). -- the :term:`view name` is "buz.txt" +- The :term:`view name` is "buz.txt". -- the :term:`subpath` is an empty sequence ( ``()`` ). +- The :term:`subpath` is an empty sequence ( ``()`` ). At this point, traversal has ended, and :term:`view lookup` begins. Because it's the "context" resource, the view lookup machinery examines the "biz" resource to find out what "type" it is. Let's say it finds that the resource is a ``Biz`` type (because "biz" is an instance of the Python class -``Biz``). Using the :term:`view name` (``buz.txt``) and the type, view -lookup asks the :term:`application registry` this question: +``Biz``). Using the :term:`view name` (``buz.txt``) and the type, view lookup +asks the :term:`application registry` this question: - Please find me a :term:`view callable` registered with a :term:`view - configuration` with the name ``buz.txt`` that can be used for class - ``Biz``. + configuration` with the name ``buz.txt`` that can be used for class ``Biz``. -Let's say that question is answered by the application registry; in such a -situation, the application registry returns a :term:`view callable`. The -view callable is then called with the current :term:`WebOb` :term:`request` -as the sole argument: ``request``; it is expected to return a response. +Let's say that question is answered by the application registry. In such a +situation, the application registry returns a :term:`view callable`. The view +callable is then called with the current :term:`WebOb` :term:`request` as the +sole argument, ``request``. It is expected to return a response. -.. sidebar:: The Example View Callables Accept Only a Request; How Do I Access the Context Resource? +.. sidebar:: The Example View Callables Accept Only a Request; How Do I Access + the Context Resource? - Most of the examples in this book assume that a view callable is typically - passed only a :term:`request` object. Sometimes your view callables need - access to the :term:`context` resource, especially when you use - :term:`traversal`. You might use a supported alternate view callable + Most of the examples in this documentation assume that a view callable is + typically passed only a :term:`request` object. Sometimes your view + callables need access to the :term:`context` resource, especially when you + use :term:`traversal`. You might use a supported alternative view callable argument list in your view callables such as the ``(context, request)`` - calling convention described in - :ref:`request_and_context_view_definitions`. But you don't need to if you - don't want to. In view callables that accept only a request, the - :term:`context` resource found by traversal is available as the - ``context`` attribute of the request object, e.g. ``request.context``. - The :term:`view name` is available as the ``view_name`` attribute of the - request object, e.g. ``request.view_name``. Other :app:`Pyramid` - -specific request attributes are also available as described in - :ref:`special_request_attributes`. + calling convention described in :ref:`request_and_context_view_definitions`. + But you don't need to if you don't want to. In view callables that accept + only a request, the :term:`context` resource found by traversal is available + as the ``context`` attribute of the request object, e.g., + ``request.context``. The :term:`view name` is available as the ``view_name`` + attribute of the request object, e.g., ``request.view_name``. Other + :app:`Pyramid`-specific request attributes are also available as described + in :ref:`special_request_attributes`. .. index:: single: resource interfaces .. _using_resource_interfaces: -Using Resource Interfaces In View Configuration +Using Resource Interfaces in View Configuration ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Instead of registering your views with a ``context`` that names a Python @@ -460,18 +447,17 @@ resource *class*, you can optionally register a view callable with a arbitrarily to any resource object. View lookup treats context interfaces specially, and therefore the identity of a resource can be divorced from that of the class which implements it. As a result, associating a view with an -interface can provide more flexibility for sharing a single view between two -or more different implementations of a resource type. For example, if two -resource objects of different Python class types share the same interface, -you can use the same view configuration to specify both of them as a -``context``. +interface can provide more flexibility for sharing a single view between two or +more different implementations of a resource type. For example, if two +resource objects of different Python class types share the same interface, you +can use the same view configuration to specify both of them as a ``context``. In order to make use of interfaces in your application during view dispatch, you must create an interface and mark up your resource classes or instances with interface declarations that refer to this interface. -To attach an interface to a resource *class*, you define the interface and -use the :func:`zope.interface.implementer` class decorator to associate the +To attach an interface to a resource *class*, you define the interface and use +the :func:`zope.interface.implementer` class decorator to associate the interface with the class. .. code-block:: python @@ -488,9 +474,9 @@ interface with the class. pass To attach an interface to a resource *instance*, you define the interface and -use the :func:`zope.interface.alsoProvides` function to associate the -interface with the instance. This function mutates the instance in such a -way that the interface is attached to it. +use the :func:`zope.interface.alsoProvides` function to associate the interface +with the instance. This function mutates the instance in such a way that the +interface is attached to it. .. code-block:: python :linenos: @@ -509,13 +495,13 @@ way that the interface is attached to it. alsoProvides(hello, IHello) return hello -Regardless of how you associate an interface, with a resource instance, or a -resource class, the resulting code to associate that interface with a view +Regardless of how you associate an interface—with either a resource instance +or a resource class—the resulting code to associate that interface with a view callable is the same. Assuming the above code that defines an ``IHello`` interface lives in the root of your application, and its module is named "resources.py", the interface declaration below will associate the -``mypackage.views.hello_world`` view with resources that implement, or -provide, this interface. +``mypackage.views.hello_world`` view with resources that implement, or provide, +this interface. .. code-block:: python :linenos: @@ -525,20 +511,18 @@ provide, this interface. config.add_view('mypackage.views.hello_world', name='hello.html', context='mypackage.resources.IHello') -Any time a resource that is determined to be the :term:`context` provides -this interface, and a view named ``hello.html`` is looked up against it as -per the URL, the ``mypackage.views.hello_world`` view callable will be -invoked. - -Note, in cases where a view is registered against a resource class, and a -view is also registered against an interface that the resource class -implements, an ambiguity arises. Views registered for the resource class take -precedence over any views registered for any interface the resource class -implements. Thus, if one view configuration names a ``context`` of both the -class type of a resource, and another view configuration names a ``context`` -of interface implemented by the resource's class, and both view -configurations are otherwise identical, the view registered for the context's -class will "win". +Any time a resource that is determined to be the :term:`context` provides this +interface, and a view named ``hello.html`` is looked up against it as per the +URL, the ``mypackage.views.hello_world`` view callable will be invoked. + +Note, in cases where a view is registered against a resource class, and a view +is also registered against an interface that the resource class implements, an +ambiguity arises. Views registered for the resource class take precedence over +any views registered for any interface the resource class implements. Thus, if +one view configuration names a ``context`` of both the class type of a +resource, and another view configuration names a ``context`` of interface +implemented by the resource's class, and both view configurations are otherwise +identical, the view registered for the context's class will "win". For more information about defining resources with interfaces for use within view configuration, see :ref:`resources_which_implement_interfaces`. @@ -558,4 +542,3 @@ traversal, such as traversal invocation from within application code. The :meth:`pyramid.request.Request.resource_url` method generates a URL when given a resource retrieved from a resource tree. - |