.. _routing:

===========
URL Routing
===========

.. module:: werkzeug.routing

When it comes to combining multiple controller or view functions (however
you want to call them), you need a dispatcher.  A simple way would be
applying regular expression tests on ``PATH_INFO`` and call registered
callback functions that return the value.

Werkzeug provides a much more powerful system, similar to `Routes`_.  All the
objects mentioned on this page must be imported from :mod:`werkzeug.routing`, not
from :mod:`werkzeug`!

.. _Routes: http://routes.groovie.org/


Quickstart
==========

Here a simple example which could be the URL definition for a blog::

    from werkzeug.routing import Map, Rule, NotFound, RequestRedirect

    url_map = Map([
        Rule('/', endpoint='blog/index'),
        Rule('/<int:year>/', endpoint='blog/archive'),
        Rule('/<int:year>/<int:month>/', endpoint='blog/archive'),
        Rule('/<int:year>/<int:month>/<int:day>/', endpoint='blog/archive'),
        Rule('/<int:year>/<int:month>/<int:day>/<slug>',
             endpoint='blog/show_post'),
        Rule('/about', endpoint='blog/about_me'),
        Rule('/feeds/', endpoint='blog/feeds'),
        Rule('/feeds/<feed_name>.rss', endpoint='blog/show_feed')
    ])

    def application(environ, start_response):
        urls = url_map.bind_to_environ(environ)
        try:
            endpoint, args = urls.match()
        except HTTPException, e:
            return e(environ, start_response)
        start_response('200 OK', [('Content-Type', 'text/plain')])
        return ['Rule points to %r with arguments %r' % (endpoint, args)]

So what does that do?  First of all we create a new :class:`Map` which stores
a bunch of URL rules.  Then we pass it a list of :class:`Rule` objects.

Each :class:`Rule` object is instantiated with a string that represents a rule
and an endpoint which will be the alias for what view the rule represents.
Multiple rules can have the same endpoint but should have different arguments
to allow URL construction.

The format for the URL rules is straightforward, but explained in detail below.

Inside the WSGI application we bind the url_map to the current request which will
return a new :class:`MapAdapter`.  This url_map adapter can then be used to match
or build domains for the current request.

The :meth:`MapAdapter.match` method can then either return a tuple in the form
``(endpoint, args)`` or raise one of the three exceptions
:exc:`~werkzeug.exceptions.NotFound`, :exc:`~werkzeug.exceptions.MethodNotAllowed`,
or :exc:`~werkzeug.exceptions.RequestRedirect`.  For more details about those
exceptions have a look at the documentation of the :meth:`MapAdapter.match` method.


Rule Format
===========

Rule strings basically are just normal URL paths with placeholders in the
format ``<converter(arguments):name>``, where converter and the arguments
are optional.  If no converter is defined, the `default` converter is used
(which means `string` in the normal configuration).

URL rules that end with a slash are branch URLs, others are leaves.  If you
have `strict_slashes` enabled (which is the default), all branch URLs that are
visited without a trailing slash will trigger a redirect to the same URL with
that slash appended.

The list of converters can be extended, the default converters are explained
below.


Builtin Converters
==================

Here a list of converters that come with Werkzeug:

.. autoclass:: UnicodeConverter

.. autoclass:: PathConverter

.. autoclass:: AnyConverter

.. autoclass:: IntegerConverter

.. autoclass:: FloatConverter

.. admonition:: Important

    Werkzeug evaluates converter arguments as if they are Python method calls.
    Thus, you should **never** create rules from user submitted data since
    they could insert arbitrary Python code in the parameters part.

    As a matter of fact this is a legal definition and sets fixed_digits to 2:

    .. sourcecode:: python

        url_map = Map([
            Rule('/picture/<int(fixed_digits=1 + 1):id>.png',
                 endpoint='view_image')
        ])

    However, evaluating Python expressions is currently an implementation
    detail and might be unavailable in the future.


Maps, Rules and Adapters
========================

.. autoclass:: Map
   :members:

.. autoclass:: MapAdapter
   :members:

.. autoclass:: Rule
   :members: empty


Rule Factories
==============

.. autoclass:: RuleFactory
   :members: get_rules

.. autoclass:: Subdomain

.. autoclass:: Submount

.. autoclass:: EndpointPrefix


Rule Templates
==============

.. autoclass:: RuleTemplate


Custom Converters
=================

You can easily add custom converters.  The only thing you have to do is to
subclass :class:`BaseConverter` and pass that new converter to the url_map.
A converter has to provide two public methods: `to_python` and `to_url`,
as well as a member that represents a regular expression.  Here is a small
example::

    from random import randrange
    from werkzeug.routing import Rule, Map, BaseConverter, ValidationError

    class BooleanConverter(BaseConverter):

        def __init__(self, url_map, randomify=False):
            super(BooleanConverter, self).__init__(url_map)
            self.randomify = randomify
            self.regex = '(?:yes|no|maybe)'

        def to_python(self, value):
            if value == 'maybe':
                if self.randomify:
                    return not randrange(2)
                raise ValidationError()
            return value == 'yes'

        def to_url(self, value):
            return value and 'yes' or 'no'

    url_map = Map([
        Rule('/vote/<bool:werkzeug_rocks>', endpoint='vote'),
        Rule('/vote/<bool(randomify=True):foo>', endpoint='foo')
    ], converters={'bool': BooleanConverter})

If you want that converter to be the default converter, name it ``'default'``.
