URL Dispatch

URL dispatch provides a simple way to map URLs to view code using a simple pattern matching language. An ordered set of patterns is checked one by one. If one of the patterns matches the path information associated with a request, a particular view callable is invoked. A view callable is a specific bit of code, defined in your application, that receives the request and returns a response object.

High-Level Operational Overview

If any route configuration is present in an application, the Pyramid Router checks every incoming request against an ordered set of URL matching patterns present in a route map.

If any route pattern matches the information in the request, Pyramid will invoke the view lookup process to find a matching view.

If no route pattern in the route map matches the information in the request provided in your application, Pyramid will fail over to using traversal to perform resource location and view lookup.

Route Configuration

Route configuration is the act of adding a new route to an application. A route has a name, which acts as an identifier to be used for URL generation. The name also allows developers to associate a view configuration with the route. A route also has a pattern, meant to match against the PATH_INFO portion of a URL (the portion following the scheme and port, e.g., /foo/bar in the URL http://localhost:8080/foo/bar). It also optionally has a factory and a set of route predicate attributes.

Configuring a Route to Match a View

The pyramid.config.Configurator.add_route() method adds a single route configuration to the application registry. Here's an example:

# "config" below is presumed to be an instance of the
# pyramid.config.Configurator class; "myview" is assumed
# to be a "view callable" function
from views import myview
config.add_route('myroute', '/prefix/{one}/{two}')
config.add_view(myview, route_name='myroute')

When a view callable added to the configuration by way of add_view() becomes associated with a route via its route_name predicate, that view callable will always be found and invoked when the associated route pattern matches during a request.

More commonly, you will not use any add_view statements in your project's "setup" code. You will instead use add_route statements, and use a scan to associate view callables with routes. For example, if this is a portion of your project's __init__.py:

config.add_route('myroute', '/prefix/{one}/{two}')

Note that we don't call add_view() in this setup code. However, the above scan execution config.scan('mypackage') will pick up each configuration decoration, including any objects decorated with the pyramid.view.view_config decorator in the mypackage Python package. For example, if you have a views.py in your package, a scan will pick up any of its configuration decorators, so we can add one there that references myroute as a route_name parameter:

from pyramid.view import view_config
from pyramid.response import Response

def myview(request):
    return Response('OK')

The above combination of add_route and scan is completely equivalent to using the previous combination of add_route and add_view.

Route Pattern Syntax

The syntax of the pattern matching language used by Pyramid URL dispatch in the pattern argument is straightforward. It is close to that of the Routes system used by Pylons.

The pattern used in route configuration may start with a slash character. If the pattern does not start with a slash character, an implicit slash will be prepended to it at matching time. For example, the following patterns are equivalent:




If a pattern is a valid URL it won't be matched against an incoming request. Instead it can be useful for generating external URLs. See External routes for details.

A pattern segment (an individual item between / characters in the pattern) may either be a literal string (e.g., foo) or it may be a replacement marker (e.g., {foo}), or a certain combination of both. A replacement marker does not need to be preceded by a / character.

A replacement marker is in the format {name}, where this means "accept any characters up to the next slash character and use this as the name matchdict value."

A replacement marker in a pattern must begin with an uppercase or lowercase ASCII letter or an underscore, and can be composed only of uppercase or lowercase ASCII letters, underscores, and numbers. For example: a, a_b, _b, and b9 are all valid replacement marker names, but 0a is not.

Changed in version 1.2: A replacement marker could not start with an underscore until Pyramid 1.2. Previous versions required that the replacement marker start with an uppercase or lowercase letter.

A matchdict is the dictionary representing the dynamic parts extracted from a URL based on the routing pattern. It is available as request.matchdict. For example, the following pattern defines one literal segment (foo) and two replacement markers (baz, and bar):


The above pattern will match these URLs, generating the following matchdicts:

foo/1/2        -> {'baz': '1', 'bar': '2'}
foo/abc/def    -> {'baz': 'abc', 'bar': 'def'}

It will not match the following patterns however:

foo/1/2/        -> No match (trailing slash)
bar/abc/def     -> First segment literal mismatch

The match for a segment replacement marker in a segment will be done only up to the first non-alphanumeric character in the segment in the pattern. So, for instance, if this route pattern was used:


The literal path /foo/biz.html will match the above route pattern, and the match result will be {'name': 'biz'}. However, the literal path /foo/biz will not match, because it does not contain a literal .html at the end of the segment represented by {name}.html (it only contains biz, not biz.html).

To capture both segments, two replacement markers can be used:


The literal path /foo/biz.html will match the above route pattern, and the match result will be {'name': 'biz', 'ext': 'html'}. This occurs because there is a literal part of . (period) between the two replacement markers {name} and {ext}.

Replacement markers can optionally specify a regular expression which will be used to decide whether a path segment should match the marker. To specify that a replacement marker should match only a specific set of characters as defined by a regular expression, you must use a slightly extended form of replacement marker syntax. Within braces, the replacement marker name must be followed by a colon, then directly thereafter, the regular expression. The default regular expression associated with a replacement marker [^/]+ matches one or more characters which are not a slash. For example, under the hood, the replacement marker {foo} can more verbosely be spelled as {foo:[^/]+}. You can change this to be an arbitrary regular expression to match an arbitrary sequence of characters, such as {foo:\d+} to match only digits.

It is possible to use two replacement markers without any literal characters between them, for instance /{foo}{bar}. However, this would be a nonsensical pattern without specifying a custom regular expression to restrict what each marker captures.

Segments must contain at least one character in order to match a segment replacement marker. For example, for the URL /abc/:

  • /abc/{foo} will not match.

  • /{foo}/ will match.

Note that values representing matched path segments will be URL-unquoted and decoded from UTF-8 into Unicode within the matchdict. So for instance, the following pattern:


When matching the following URL:


The matchdict will look like so (the value is URL-decoded / UTF-8 decoded):

{'bar': 'La Pe\xf1a'}

Literal strings in the path segment should represent the decoded value of the PATH_INFO provided to Pyramid. You don't want to use a URL-encoded value or a bytestring representing the literal encoded as UTF-8 in the pattern. For example, rather than this:


You'll want to use something like this:

/Foo Bar/{baz}

For patterns that contain "high-order" characters in its literals, you'll want to use a Unicode value as the pattern as opposed to any URL-encoded or UTF-8-encoded value. For example, you might be tempted to use a bytestring pattern like this:

/La Pe\xc3\xb1a/{x}

But this will either cause an error at startup time or it won't match properly. You'll want to use a Unicode value as the pattern instead rather than raw bytestring escapes. You can use a high-order Unicode value as the pattern by using Python source file encoding plus the "real" character in the Unicode pattern in the source, like so:

/La Peña/{x}

Or you can ignore source file encoding and use equivalent Unicode escape characters in the pattern.

/La Pe\xf1a/{x}

Dynamic segment names cannot contain high-order characters, so this applies only to literals in the pattern.

If the pattern has a * in it, the name which follows it is considered a "remainder match". A remainder match must come at the end of the pattern. Unlike segment replacement markers, it does not need to be preceded by a slash. For example:


The above pattern will match these URLs, generating the following matchdicts:

foo/1/2/           ->
         {'baz': '1', 'bar': '2', 'fizzle': ()}

foo/abc/def/a/b/c  ->
         {'baz': 'abc', 'bar': 'def', 'fizzle': ('a', 'b', 'c')}

Note that when a *stararg remainder match is matched, the value put into the matchdict is turned into a tuple of path segments representing the remainder of the path. These path segments are URL-unquoted and decoded from UTF-8 into Unicode. For example, for the following pattern:


When matching the following path:


Will generate the following matchdict:

{'fizzle': ('La Pe\xf1a', 'a', 'b', 'c')}

By default, the *stararg will parse the remainder sections into a tuple split by segment. Changing the regular expression used to match a marker can also capture the remainder of the URL, for example:


The above pattern will match these URLs, generating the following matchdicts:

foo/1/2/           -> {'baz': '1', 'bar': '2', 'fizzle': ''}
foo/abc/def/a/b/c  -> {'baz': 'abc', 'bar': 'def', 'fizzle': 'a/b/c'}

This occurs because the default regular expression for a marker is [^/]+ which will match everything up to the first /, while {fizzle:.*} will result in a regular expression match of .* capturing the remainder into a single value.

Route Declaration Ordering

Route configuration declarations are evaluated in a specific order when a request enters the system. As a result, the order of route configuration declarations is very important. The order in which route declarations are evaluated is the order in which they are added to the application at startup time. (This is unlike a different way of mapping URLs to code that Pyramid provides, named traversal, which does not depend on pattern ordering).

For routes added via the add_route method, the order that routes are evaluated is the order in which they are added to the configuration imperatively.

For example, route configuration statements with the following patterns might be added in the following order:


In such a configuration, the members/abc pattern would never be matched. This is because the match ordering will always match members/{def} first; the route configuration with members/abc will never be evaluated.

Route Configuration Arguments

Route configuration add_route statements may specify a large number of arguments. They are documented as part of the API documentation at pyramid.config.Configurator.add_route().

Many of these arguments are route predicate arguments. A route predicate argument specifies that some aspect of the request must be true for the associated route to be considered a match during the route matching process. Examples of route predicate arguments are pattern, xhr, and request_method.

Other arguments are name and factory. These arguments represent neither predicates nor view configuration information.

Route Matching

The main purpose of route configuration is to match (or not match) the PATH_INFO present in the WSGI environment provided during a request against a URL path pattern. PATH_INFO represents the path portion of the URL that was requested.

The way that Pyramid does this is very simple. When a request enters the system, for each route configuration declaration present in the system, Pyramid checks the request's PATH_INFO against the pattern declared. This checking happens in the order that the routes were declared via pyramid.config.Configurator.add_route().

When a route configuration is declared, it may contain route predicate arguments. All route predicates associated with a route declaration must be True for the route configuration to be used for a given request during a check. If any predicate in the set of route predicate arguments provided to a route configuration returns False during a check, that route is skipped and route matching continues through the ordered set of routes.

If any route matches, the route matching process stops and the view lookup subsystem takes over to find the most reasonable view callable for the matched route. Most often, there's only one view that will match (a view configured with a route_name argument matching the matched route). To gain a better understanding of how routes and views are associated in a real application, you can use the pviews command, as documented in pviews: Displaying Matching Views for a Given URL.

If no route matches after all route patterns are exhausted, Pyramid falls back to traversal to do resource location and view lookup.

The Matchdict

When the URL pattern associated with a particular route configuration is matched by a request, a dictionary named matchdict is added as an attribute of the request object. Thus, request.matchdict will contain the values that match replacement patterns in the pattern element. The keys in a matchdict will be strings. The values will be Unicode objects.


If no route URL pattern matches, the matchdict object attached to the request will be None.

The Matched Route

When the URL pattern associated with a particular route configuration is matched by a request, an object named matched_route is added as an attribute of the request object. Thus, request.matched_route will be an object implementing the IRoute interface which matched the request. The most useful attribute of the route object is name, which is the name of the route that matched.


If no route URL pattern matches, the matched_route object attached to the request will be None.

Routing Examples

Let's check out some examples of how route configuration statements might be commonly declared, and what will happen if they are matched by the information present in a request.

Example 1

The simplest route declaration which configures a route match to directly result in a particular view callable being invoked:

1config.add_route('idea', 'site/{id}')

When a route configuration with a view attribute is added to the system, and an incoming request matches the pattern of the route configuration, the view callable named as the view attribute of the route configuration will be invoked.

Recall that the @view_config is equivalent to calling config.add_view, because the config.scan() call will import mypackage.views, shown below, and execute config.add_view under the hood. Each view then maps the route name to the matching view callable. In the case of the above example, when the URL of a request matches /site/{id}, the view callable at the Python dotted path name mypackage.views.site_view will be called with the request. In other words, we've associated a view callable directly with a route pattern.

When the /site/{id} route pattern matches during a request, the site_view view callable is invoked with that request as its sole argument. When this route matches, a matchdict will be generated and attached to the request as request.matchdict. If the specific URL matched is /site/1, the matchdict will be a dictionary with a single key, id; the value will be the string '1', ex.: {'id': '1'}.

The mypackage.views module referred to above might look like so:

1from pyramid.view import view_config
2from pyramid.response import Response
5def site_view(request):
6    return Response(request.matchdict['id'])

The view has access to the matchdict directly via the request, and can access variables within it that match keys present as a result of the route pattern.

See Views, and View Configuration for more information about views.

Example 2

Below is an example of a more complicated set of route statements you might add to your application:

1config.add_route('idea', 'ideas/{idea}')
2config.add_route('user', 'users/{user}')
3config.add_route('tag', 'tags/{tag}')

Here is an example of a corresponding mypackage.views module:

 1from pyramid.view import view_config
 2from pyramid.response import Response
 5def idea_view(request):
 6    return Response(request.matchdict['idea'])
 9def user_view(request):
10    user = request.matchdict['user']
11    return Response('The user is {}.'.format(user))
14def tag_view(request):
15    tag = request.matchdict['tag']
16    return Response('The tag is {}.'.format(tag))

The above configuration will allow Pyramid to service URLs in these forms:

  • When a URL matches the pattern /ideas/{idea}, the view callable available at the dotted Python pathname mypackage.views.idea_view will be called. For the specific URL /ideas/1, the matchdict generated and attached to the request will consist of {'idea': '1'}.

  • When a URL matches the pattern /users/{user}, the view callable available at the dotted Python pathname mypackage.views.user_view will be called. For the specific URL /users/1, the matchdict generated and attached to the request will consist of {'user': '1'}.

  • When a URL matches the pattern /tags/{tag}, the view callable available at the dotted Python pathname mypackage.views.tag_view will be called. For the specific URL /tags/1, the matchdict generated and attached to the request will consist of {'tag': '1'}.

In this example we've again associated each of our routes with a view callable directly. In all cases, the request, which will have a matchdict attribute detailing the information found in the URL by the process will be passed to the view callable.

Example 3

The context resource object passed in to a view found as the result of URL dispatch will, by default, be an instance of the object returned by the root factory configured at startup time (the root_factory argument to the Configurator used to configure the application).

You can override this behavior by passing in a factory argument to the add_route() method for a particular route. The factory should be a callable that accepts a request and returns an instance of a class that will be the context resource used by the view.

An example of using a route with a factory:

1config.add_route('idea', 'ideas/{idea}', factory='myproject.resources.Idea')

The above route will manufacture an Idea resource as a context, assuming that mypackage.resources.Idea resolves to a class that accepts a request in its __init__. For example:

1class Idea(object):
2    def __init__(self, request):
3        pass

In a more complicated application, this root factory might be a class representing a SQLAlchemy model. The view mypackage.views.idea_view might look like this:

2def idea_view(request):
3    idea = request.context
4    return Response(idea)

Here, request.context is an instance of Idea. If indeed the resource object is a SQLAlchemy model, you do not even have to perform a query in the view callable, since you have access to the resource via request.context.

See Route Factories for more details about how to use route factories.

Matching the Root URL

It's not entirely obvious how to use a route pattern to match the root URL ("/"). To do so, give the empty string as a pattern in a call to add_route():

1config.add_route('root', '')

Or provide the literal string / as the pattern:

1config.add_route('root', '/')

Generating Route URLs

Use the pyramid.request.Request.route_url() method to generate URLs based on route patterns. For example, if you've configured a route with the name "foo" and the pattern "{a}/{b}/{c}", you might do this.

1url = request.route_url('foo', a='1', b='2', c='3')

This would return something like the string http://example.com/1/2/3 (at least if the current protocol and hostname implied http://example.com).

To generate only the path portion of a URL from a route, use the pyramid.request.Request.route_path() API instead of route_url().

url = request.route_path('foo', a='1', b='2', c='3')

This will return the string /1/2/3 rather than a full URL.

Replacement values passed to route_url or route_path must be Unicode or bytestrings encoded in UTF-8. One exception to this rule exists: if you're trying to replace a "remainder" match value (a *stararg replacement value), the value may be a tuple containing Unicode strings or UTF-8 strings.

Note that URLs and paths generated by route_url and route_path are always URL-quoted string types (they contain no non-ASCII characters). Therefore, if you've added a route like so:

config.add_route('la', '/La Peña/{city}')

And you later generate a URL using route_path or route_url like so:

url = request.route_path('la', city='Québec')

You will wind up with the path encoded to UTF-8 and URL-quoted like so:


If you have a *stararg remainder dynamic part of your route pattern:

config.add_route('abc', 'a/b/c/*foo')

And you later generate a URL using route_path or route_url using a string as the replacement value:

url = request.route_path('abc', foo='Québec/biz')

The value you pass will be URL-quoted except for embedded slashes in the result:


You can get a similar result by passing a tuple composed of path elements:

url = request.route_path('abc', foo=('Québec', 'biz'))

Each value in the tuple will be URL-quoted and joined by slashes in this case:


Static Routes

Routes may be added with a static keyword argument. For example:

1config = Configurator()
2config.add_route('page', '/page/{action}', static=True)

Routes added with a True static keyword argument will never be considered for matching at request time. Static routes are useful for URL generation purposes only. As a result, it is usually nonsensical to provide other non-name and non-pattern arguments to add_route() when static is passed as True, as none of the other arguments will ever be employed. A single exception to this rule is use of the pregenerator argument, which is not ignored when static is True.

External routes are implicitly static.

New in version 1.1: the static argument to add_route().

External Routes

New in version 1.5.

Route patterns that are valid URLs, are treated as external routes. Like static routes they are useful for URL generation purposes only and are never considered for matching at request time.

1>>> config = Configurator()
2>>> config.add_route('youtube', 'https://youtube.com/watch/{video_id}')
4>>> request.route_url('youtube', video_id='oHg5SJYRHA0')
5>>> "https://youtube.com/watch/oHg5SJYRHA0"

Most pattern replacements and calls to pyramid.request.Request.route_url() will work as expected. However, calls to pyramid.request.Request.route_path() against external patterns will raise an exception, and passing _app_url to route_url() to generate a URL against a route that has an external pattern will also raise an exception.

Redirecting to Slash-Appended Routes

For behavior like Django's APPEND_SLASH=True, use the append_slash argument to pyramid.config.Configurator.add_notfound_view() or the equivalent append_slash argument to the pyramid.view.notfound_view_config decorator.

Adding append_slash=True is a way to automatically redirect requests where the URL lacks a trailing slash, but requires one to match the proper route. When configured, along with at least one other route in your application, this view will be invoked if the value of PATH_INFO does not already end in a slash, and if the value of PATH_INFO plus a slash matches any route's pattern. In this case it does an HTTP redirect to the slash-appended PATH_INFO. In addition you may pass anything that implements pyramid.interfaces.IResponse which will then be used in place of the default class (pyramid.httpexceptions.HTTPFound).

Let's use an example. If the following routes are configured in your application:

 1from pyramid.httpexceptions import HTTPNotFound
 3def notfound(request):
 4    return HTTPNotFound()
 6def no_slash(request):
 7    return Response('No slash')
 9def has_slash(request):
10    return Response('Has slash')
12def main(g, **settings):
13    config = Configurator()
14    config.add_route('noslash', 'no_slash')
15    config.add_route('hasslash', 'has_slash/')
16    config.add_view(no_slash, route_name='noslash')
17    config.add_view(has_slash, route_name='hasslash')
18    config.add_notfound_view(notfound, append_slash=True)

If a request enters the application with the PATH_INFO value of /no_slash, the first route will match and the browser will show "No slash". However, if a request enters the application with the PATH_INFO value of /no_slash/, no route will match, and the slash-appending not found view will not find a matching route with an appended slash. As a result, the notfound view will be called and it will return a "Not found" body.

If a request enters the application with the PATH_INFO value of /has_slash/, the second route will match. If a request enters the application with the PATH_INFO value of /has_slash, a route will be found by the slash-appending Not Found View. An HTTP redirect to /has_slash/ will be returned to the user's browser. As a result, the notfound view will never actually be called.

The following application uses the pyramid.view.notfound_view_config and pyramid.view.view_config decorators and a scan to do exactly the same job:

 1from pyramid.httpexceptions import HTTPNotFound
 2from pyramid.view import notfound_view_config, view_config
 5def notfound(request):
 6    return HTTPNotFound()
 9def no_slash(request):
10    return Response('No slash')
13def has_slash(request):
14    return Response('Has slash')
16def main(g, **settings):
17    config = Configurator()
18    config.add_route('noslash', 'no_slash')
19    config.add_route('hasslash', 'has_slash/')
20    config.scan()


You should not rely on this mechanism to redirect POST requests. The redirect of the slash-appending Not Found View will turn a POST request into a GET, losing any POST data in the original request.

See pyramid.view and Changing the Not Found View for a more general description of how to configure a view and/or a Not Found View.

Debugging Route Matching

It's useful to be able to take a peek under the hood when requests that enter your application aren't matching your routes as you expect them to. To debug route matching, use the PYRAMID_DEBUG_ROUTEMATCH environment variable or the pyramid.debug_routematch configuration file setting (set either to true). Details of the route matching decision for a particular request to the Pyramid application will be printed to the stderr of the console which you started the application from. For example:

 1PYRAMID_DEBUG_ROUTEMATCH=true $VENV/bin/pserve development.ini
 2Starting server in PID 13586.
 3serving on view at
 42010-12-16 14:45:19,956 no route matched for url \
 5                                    http://localhost:6543/wontmatch
 62010-12-16 14:45:20,010 no route matched for url \
 7                            http://localhost:6543/favicon.ico
 82010-12-16 14:41:52,084 route matched for url \
 9                            http://localhost:6543/static/logo.png; \
10                            route_name: 'static/', ....

See Environment Variables and .ini File Settings for more information about how and where to set these values.

You can also use the proutes command to see a display of all the routes configured in your application. For more information, see proutes: Displaying All Application Routes.

Using a Route Prefix to Compose Applications

New in version 1.2.

The pyramid.config.Configurator.include() method allows configuration statements to be included from separate files. See Rules for Building an Extensible Application for information about this method. Using pyramid.config.Configurator.include() allows you to build your application from small and potentially reusable components.

The pyramid.config.Configurator.include() method accepts an argument named route_prefix which can be useful to authors of URL-dispatch-based applications. If route_prefix is supplied to the include method, it must be a string. This string represents a route prefix that will be prepended to all route patterns added by the included configuration. Any calls to pyramid.config.Configurator.add_route() within the included callable will have their pattern prefixed with the value of route_prefix. This can be used to help mount a set of routes at a different location than the included callable's author intended while still maintaining the same route names. For example:

1from pyramid.config import Configurator
3def users_include(config):
4    config.add_route('show_users', '/show')
6def main(global_config, **settings):
7    config = Configurator()
8    config.include(users_include, route_prefix='/users')

In the above configuration, the show_users route will have an effective route pattern of /users/show instead of /show because the route_prefix argument will be prepended to the pattern. The route will then only match if the URL path is /users/show, and when the pyramid.request.Request.route_url() function is called with the route name show_users, it will generate a URL with that same path.

To create a route that matches requests to the route_prefix without a trailing slash, pass inherit_slash=True to the call to add_route.

1from pyramid.config import Configurator
3def users_include(config):
4    config.add_route('show_users', '', inherit_slash=True)
6def main(global_config, **settings):
7    config = Configurator()
8    config.include(users_include, route_prefix='/users')

The above configuration will match /users instead of /users/.

Route prefixes are recursive, so if a callable executed via an include itself turns around and includes another callable, the second-level route prefix will be prepended with the first:

 1from pyramid.config import Configurator
 3def timing_include(config):
 4    config.add_route('show_times', '/times')
 6def users_include(config):
 7    config.add_route('show_users', '/show')
 8    config.include(timing_include, route_prefix='/timing')
10def main(global_config, **settings):
11    config = Configurator()
12    config.include(users_include, route_prefix='/users')

In the above configuration, the show_users route will still have an effective route pattern of /users/show. The show_times route, however, will have an effective pattern of /users/timing/times.

Route prefixes have no impact on the requirement that the set of route names in any given Pyramid configuration must be entirely unique. If you compose your URL dispatch application out of many small subapplications using pyramid.config.Configurator.include(), it's wise to use a dotted name for your route names so they'll be unlikely to conflict with other packages that may be added in the future. For example:

 1from pyramid.config import Configurator
 3def timing_include(config):
 4    config.add_route('timing.show_times', '/times')
 6def users_include(config):
 7    config.add_route('users.show_users', '/show')
 8    config.include(timing_include, route_prefix='/timing')
10def main(global_config, **settings):
11    config = Configurator()
12    config.include(users_include, route_prefix='/users')

A convenience context manager exists to set the route prefix for any pyramid.config.Configurator.add_route() or pyramid.config.Configurator.include() calls within the context.

 1from pyramid.config import Configurator
 3def timing_include(config):
 4    config.add_route('timing.show_times', '/times')
 6def main(global_config, **settings)
 7    config = Configurator()
 8    with config.route_prefix_context('/timing'):
 9        config.include(timing_include)
10        config.add_route('timing.average', '/average')

Custom Route Predicates

A predicate is a callable that accepts two arguments: a dictionary conventionally named info, and the current request object.

The info dictionary has a number of contained values, including match and route. match is a dictionary which represents the arguments matched in the URL by the route. route is an object representing the route which was matched (see pyramid.interfaces.IRoute for the API of such a route object).

info['match'] is useful when predicates need access to the route match. Imagine you want to define a route when a part of the URL matches some specific values. You could define three view configurations, each one with its own match_param value (see Predicate Arguments), but you want to think of it as one route, and associate it with one view. See this code:

 1class AnyOfPredicate:
 2    def __init__(self, val, info):
 3        self.segment_name = val[0]
 4        self.allowed = tuple(val[1:])
 6    def text(self):
 7        args = (self.segment_name,) + self.allowed
 8        return 'any_of = %s' % (args,)
10    phash = text
12    def __call__(self, info, request):
13        return info['match'][self.segment_name] in self.allowed
16config.add_route_predicate('any_of', AnyOfPredicate)
17config.add_route('route_to_num', '/{num}', any_of=('num', 'one', 'two', 'three'))

We register this class as a predicate factory with the any_of keyword argument name. Then we use that new keyword argument with add_route(). When the route is requested, Pyramid instantiates the AnyOfPredicate class using the value passed to the any_of argument. (The info parameter passed to the factory contains some metadata, you can ignore it for now.) The resulting instance is a predicate. It will determine whether incoming requests satisfy its condition. In the example above, a request for /three would match the route's URL pattern and satisfy the route's predicate because three is one of the allowed values, so the route would be matched. However a request for /millions will match the route's URL pattern but would not satisfy the route's predicate, and the route would not be matched.

A custom route predicate may also modify the match dictionary. For instance, a predicate might do some type conversion of values:

 1class IntegersPredicate:
 2    def __init__(self, val, info):
 3        self.segment_names = val
 5    def text(self):
 6        return 'integers = %s' % (self.segment_names,)
 8    phash = text
10    def __call__(self, info, request):
11        match = info['match']
12        for segment_name in self.segment_names:
13            try:
14                match[segment_name] = int(match[segment_name])
15            except (TypeError, ValueError):
16                pass
17        return True
20config.add_route_predicate('integers', IntegersPredicate)
21config.add_route('ymd', '/{year}/{month}/{day}',
22                 integers=('year', 'month', 'day'))

Note that a conversion predicate is still a predicate, so it must return True or False. A predicate that does only conversion, such as the one we demonstrate above, should unconditionally return True.

To avoid the try/except uncertainty, the route pattern can contain regular expressions specifying requirements for that marker. For instance:

 1class IntegersPredicate:
 2    def __init__(self, val, info):
 3        self.segment_names = val
 5    def text(self):
 6        return 'integers = %s' % (self.segment_names,)
 8    phash = text
10    def __call__(self, info, request):
11        match = info['match']
12        for segment_name in self.segment_names:
13            match[segment_name] = int(match[segment_name])
14        return True
17config.add_route_predicate('integers', IntegersPredicate)
18config.add_route('ymd', r'/{year:\d+}/{month:\d+}/{day:\d+}',
19                 integers=('year', 'month', 'day'))

Now the try/except is no longer needed because the route will not match at all unless these markers match \d+ which requires them to be valid digits for an int type conversion.

The match dictionary passed within info to each predicate attached to a route will be the same dictionary. Therefore, when registering a custom predicate which modifies the match dict, the code registering the predicate should usually arrange for the predicate to be the last custom predicate in the custom predicate list. Otherwise, custom predicates which fire subsequent to the predicate which performs the match modification will receive the modified match dictionary.


It is a poor idea to rely on ordering of custom predicates to build a conversion pipeline, where one predicate depends on the side effect of another. For instance, it's a poor idea to register two custom predicates, one which handles conversion of a value to an int, the next which handles conversion of that integer to some custom object. Just do all that in a single custom predicate.

The route object in the info dict is an object that has two useful attributes: name and pattern. The name attribute is the route name. The pattern attribute is the route pattern. Here's an example of using the route in a set of route predicates:

 1class TwentyTenPredicate:
 2    def __init__(self, val, info):
 3        pass
 5    def text(self):
 6        return "twenty_ten = True"
 8    phash = text
10    def __call__(self, info, request):
11        if info['route'].name in ('ymd', 'ym', 'y'):
12            return info['match']['year'] == '2010'
14config.add_route_predicate('twenty_ten', TwentyTenPredicate)
15config.add_route('y', '/{year}', twenty_ten=True)
16config.add_route('ym', '/{year}/{month}', twenty_ten=True)
17config.add_route('ymd', '/{year}/{month}/{day}', twenty_ten=True)

The above predicate, when added to a number of route configurations ensures that the year match argument is 2010 if and only if the route name is ymd, ym, or y.

The text method is a way to caption the predicates. This will help you with the pviews command (see proutes: Displaying All Application Routes) and the pyramid_debugtoolbar.

The phash ("predicate hash") method should return a string that uniquely identifies a specific predicate. A good way to do that is to use the same argument name and value that are in the call to add_route, like in the examples above.

See also

See Adding a Custom View, Route, or Subscriber Predicate for more information about custom view, route, and subscriber predicates.

See also pyramid.interfaces.IRoute for more API documentation about route objects.

Route Factories

Although it is not a particularly common need in basic applications, a "route" configuration declaration can mention a "factory". When a route matches a request, and a factory is attached to the route, the root factory passed at startup time to the Configurator is ignored. Instead the factory associated with the route is used to generate a root object. This object will usually be used as the context resource of the view callable ultimately found via view lookup.

1config.add_route('abc', '/abc',
2                 factory='myproject.resources.root_factory')
3config.add_view('myproject.views.theview', route_name='abc')

The factory can either be a Python object or a dotted Python name (a string) which points to such a Python object, as it is above.

In this way, each route can use a different factory, making it possible to supply a different context resource object to the view related to each particular route.

A factory must be a callable which accepts a request and returns an arbitrary Python object. For example, the below class can be used as a factory:

1class Mine(object):
2    def __init__(self, request):
3        pass

A route factory is actually conceptually identical to the root factory described at The Resource Tree.

Supplying a different resource factory for each route is useful when you're trying to use a Pyramid authorization policy to provide declarative, "context sensitive" security checks. Each resource can maintain a separate ACL, as documented in Using Pyramid Security with URL Dispatch. It is also useful when you wish to combine URL dispatch with traversal as documented within Combining Traversal and URL Dispatch.

Using Pyramid Security with URL Dispatch

Pyramid provides its own security framework which consults an authorization policy before allowing any application code to be called. This framework operates in terms of an access control list, which is stored as an __acl__ attribute of a resource object. A common thing to want to do is to attach an __acl__ to the resource object dynamically for declarative security purposes. You can use the factory argument that points at a factory which attaches a custom __acl__ to an object at its creation time.

Such a factory might look like so:

1class Article(object):
2    def __init__(self, request):
3        matchdict = request.matchdict
4        article = matchdict.get('article', None)
5        if article == '1':
6            self.__acl__ = [ (Allow, 'editor', 'view') ]

If the route archives/{article} is matched, and the article number is 1, Pyramid will generate an Article context resource with an ACL on it that allows the editor principal the view permission. Obviously you can do more generic things than inspect the route's match dict to see if the article argument matches a particular string. Our sample Article factory class is not very ambitious.


See Security for more information about Pyramid security and ACLs.

Route View Callable Registration and Lookup Details

When a request enters the system which matches the pattern of the route, the usual result is simple: the view callable associated with the route is invoked with the request that caused the invocation.

For most usage, you needn't understand more than this. How it works is an implementation detail. In the interest of completeness, however, we'll explain how it does work in this section. You can skip it if you're uninterested.

When a view is associated with a route configuration, Pyramid ensures that a view configuration is registered that will always be found when the route pattern is matched during a request. To do so:

  • A special route-specific interface is created at startup time for each route configuration declaration.

  • When an add_view statement mentions a route name attribute, a view configuration is registered at startup time. This view configuration uses a route-specific interface as a request type.

  • At runtime, when a request causes any route to match, the request object is decorated with the route-specific interface.

  • The fact that the request is decorated with a route-specific interface causes the view lookup machinery to always use the view callable registered using that interface by the route configuration to service requests that match the route pattern.

As we can see from the above description, technically, URL dispatch doesn't actually map a URL pattern directly to a view callable. Instead URL dispatch is a resource location mechanism. A Pyramid resource location subsystem (i.e., URL dispatch or traversal) finds a resource object that is the context of a request. Once the context is determined, a separate subsystem named view lookup is then responsible for finding and invoking a view callable based on information available in the context and the request. When URL dispatch is used, the resource location and view lookup subsystems provided by Pyramid are still being utilized, but in a way which does not require a developer to understand either of them in detail.

If no route is matched using URL dispatch, Pyramid falls back to traversal to handle the request.


A tutorial showing how URL dispatch can be used to create a Pyramid application exists in SQLAlchemy + URL dispatch wiki tutorial.