Configuring a Handler via ZCML

Instead of using the imperative pyramid.config.Configurator.add_handler() method to add a new route, you can alternately use ZCML.

Warning

ZCML works under Python 2.6 and 2.7; it, however, does not work under Python 3.2 or any other version of Python 3.

Using The handler ZCML Directive statements in a ZCML file used by your application is a sign that you’re using URL dispatch. For example, the following ZCML declaration causes a route to be added to the application.

<handler
  route_name="myroute"
  pattern="/prefix/{action}"
  handler=".handlers.MyHandler"
 />

Note

Values prefixed with a period (.) within the values of ZCML attributes such as the handler attribute of a handler directive mean “relative to the Python package directory in which this ZCML file is stored”. So if the above handler declaration was made inside a configure.zcml file that lived in the hello package, you could replace the relative .views.MyHandler with the absolute hello.views.MyHandler Either the relative or absolute form is functionally equivalent. It’s often useful to use the relative form, in case your package’s name changes. It’s also shorter to type.

The order that the routes attached to handlers are evaluated when declarative configuration is used is the order that they appear relative to each other in the ZCML file.

See Using The handler ZCML Directive for full handler ZCML directive documentation.

Using The handler ZCML Directive

The handler directive adds the configuration of a view handler to the application registry. It is a declarative analogue of the pyramid_handlers.add_handler() directive.

Example

Do the following from within a Pyramid application to use the handler ZCML directive.

<include package="pyramid_handlers" file="meta.zcml"/>

<handler
   route_name="foo"
   pattern="/foo/{action}"
   handler="some.module.SomeClass"/>

Attributes

route_name

The name of the route, e.g. myroute. This attribute is required. It must be unique among all defined handler and route names in a given configuration.

pattern

The pattern of the route e.g. ideas/{idea}. This attribute is required. See route_pattern_syntax for information about the syntax of route patterns. The name {action} is treated specially in handler patterns. See Handler Registration Using add_handler() for a discussion of how {action} in handler patterns is treated.

handler

A dotted Python name to the handler class.

action

If the action name is not specified in the pattern, use this name as the handler action (method name).

factory

The dotted Python name to a function that will generate a Pyramid context object when the associated route matches. e.g. mypackage.resources.MyResource. If this argument is not specified, a default root factory will be used.

xhr

This value should be either True or False. If this value is specified and is True, the request must possess an HTTP_X_REQUESTED_WITH (aka X-Requested-With) header for this route to match. This is useful for detecting AJAX requests issued from jQuery, Prototype and other Javascript libraries. If this predicate returns false, route matching continues.

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).

The syntax of the traverse argument is the same as it is for pattern. For example, if the pattern provided to the route directive is articles/{article}/edit, and the traverse argument provided to the route directive is /{article}, when a request comes in that causes the route to match in such a way that the article match value is ‘1’ (when the request URI is /articles/1/edit), the traversal path will be generated as /1. This means that the root object’s __getitem__ will be called with the name 1 during the traversal phase. If the 1 object exists, it will become the context of the request. traversal_chapter has more information about traversal.

If the traversal path contains segment marker names which are not present in the pattern argument, a runtime error will occur. The traverse pattern should not contain segment markers that do not exist in the pattern.

A similar combining of routing and traversal is available when a route is matched which contains a *traverse remainder marker in its pattern (see using_traverse_in_a_route_pattern). The traverse argument to the route directive allows you to associate route patterns with an arbitrary traversal path without using a a *traverse remainder marker; instead you can use other match information.

Note that the traverse argument to the handler directive is ignored when attached to a route that has a *traverse remainder marker in its pattern.

request_method

A string representing an HTTP method name, e.g. GET, POST, HEAD, DELETE, PUT. If this argument is not specified, this route will match if the request has any request method. If this predicate returns false, route matching continues.

path_info

The value of this attribute represents a regular expression pattern that will be tested against the PATH_INFO WSGI environment variable. If the regex matches, this predicate will be true. If this predicate returns false, route matching continues.

request_param

This value can be any string. A view declaration with this attribute ensures that the associated route will only match 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 route to “match” the current request. If this predicate returns false, route matching continues.

header

The value of this attribute represents an HTTP header name or a header name/value pair. If the value contains a : (colon), it will be considered a name/value pair (e.g. User-Agent:Mozilla/.* or Host:localhost). The value of an attribute that represent a name/value pair should be a regular expression. If the value does not contain a colon, the entire value will be considered to be the header name (e.g. If-Modified-Since). If the value evaluates to a header name only without a value, the header specified by the name must be present in the request for this predicate to be true. If the value evaluates to a header name/value pair, the header specified by the name must be present in the request and the regular expression specified as the value must match the header value. Whether or not the value represents a header name or a header name/value pair, the case of the header name is not significant. If this predicate returns false, route matching continues.

accept

The value of this attribute represents a match query for one or more mimetypes in the Accept HTTP request header. If this value is specified, it must be in one of the following forms: a mimetype match token in the form text/plain, a wildcard mimetype match token in the form text/* or a match-all wildcard mimetype match token in the form */*. If any of the forms matches the Accept header of the request, this predicate will be true. If this predicate returns false, route matching continues.

custom_predicates

This value should be a sequence of references to custom predicate callables. Use custom predicates when no set of predefined predicates does what you need. Custom predicates can be combined with predefined predicates as necessary. Each custom predicate callable should accept two arguments: info and request and should return either True or False after doing arbitrary evaluation of the info and/or the request. If all custom and non-custom predicate callables return True the associated route will be considered viable for a given request. If any predicate callable returns False, route matching continues. Note that the value info passed to a custom route predicate is a dictionary containing matching information; see custom_route_predicates for more information about info.

Alternatives

You can also add a route configuration via:

• Using the pyramid.config.Configurator.add_handler() method.

See Also

See also views_chapter.