--- django: main at 4fab678a0739d54401ccee7eb587553657c9f76e (2026-09-26), on its way to 6.2 --- # The URL checks, and listing the patterns What goes over the whole tree with no path or name in hand: the system checks tagged urls, in which every resolver and pattern checks itself, and the tools that list a project's addresses, `extract_views_from_urlpatterns`, `simplify_regex` and the command listurls. Resolving looks at as much of the tree as one path needs. Other code goes over all of it, entry by entry: the building of the tables for reversing, the checks that look for mistakes in a URLconf when a management command runs them, and the tools that print what addresses a project has. This section has the checks and the tools, and both are walks down the same lists `URLResolver.resolve` searches. ## The checks `django/core/checks/urls.py` registers four functions under the tag urls. How the system checks are registered and run, and which commands run them, is in [The system checks](../commands/checks.md). All but the one about settings do nothing in a project that has no `ROOT_URLCONF`. - `check_url_config` asks the tree to check itself. It gets the root resolver from `get_resolver` and passes it to `check_resolver`, which calls the `check` method of whatever it is given. `URLResolver.check` passes each of its entries to `check_resolver` in turn, so the walk goes down through every include. A `URLPattern` checks its name, has its matcher check the route, and checks its view. An entry with neither a `check` method nor a `resolve` method is not a pattern at all, and is reported as that (`django/core/checks/urls.py:check_url_config`, `django/core/checks/urls.py:check_resolver`, `django/urls/resolvers.py:URLResolver.check`, `django/urls/resolvers.py:URLPattern.check`). - `check_url_namespaces_unique` collects every chain of instance namespaces in the tree, each namespace joined to those above it with colons, and warns of any that occurs more than once (`django/core/checks/urls.py:check_url_namespaces_unique`). - `check_url_settings` looks at `settings.STATIC_URL` and `settings.MEDIA_URL`, each of which must end in a slash if it is set (`django/core/checks/urls.py:check_url_settings`). - `check_custom_error_handlers` tries the error views. For each of the four it asks the root resolver for the view, as the handler would when a request failed, and then tests whether the view accepts the right number of positional arguments: two, the request and the exception, or for the 500 view one (`django/core/checks/urls.py:check_custom_error_handlers`). The recording has a URLconf with one of each mistake, and calls the four functions over it one at a time. The view it names for 403 takes the request and nothing else, and the module has no view of the name it gives for 404. ```python # museum/urls_mistakes.py cafe_patterns = [ path("", views.shop, name="cafe"), ] terrace_patterns = [ path("/seats", views.shop, name="seats"), ] urlpatterns = [ path("/lost", views.entrance, name="lost"), path("cloakroom/", views.entrance, name="cloak:room"), path("^lifts/$", views.entrance, name="lifts"), path("stairs//', None, 'tickets') (views.tickets, 'tickets///', None, 'tickets') (views.wing, 'east/', ['east'], 'wing') (views.room, 'east/rooms//', ['east'], 'room') (views.track, 'east/rooms//audio//', ['east', 'audio'], 'track') ... (views.shop, 'shop/', [], 'shop') (views.item, 'shop//', [], 'item') (views.plan, '^plans/(?P[0-9])(?:\\.(?Ppdf|svg))?$', None, 'plan') (views.download, 'files/', None, 'download') ``` The third item is `None` for a pattern in the list the walk began with, and a list, which may be empty, for a pattern under an include. Each address is the routes as written, joined: a route's parameters are still in angle brackets, and a regular expression is still a regular expression. `simplify_regex` makes the second kind readable. It deletes each group written `(?:…)`, with whatever is inside it, and replaces each named group with its name in angle brackets and each group that is left with ``. It takes out the anchors `^`, `$`, `\A`, `\Z`, `\b` and `\B` and the quantifiers `?`, `*` and `+` where they stand unescaped; an escaped `^`, `$`, `?`, `*` or `+` keeps its character and loses its backslash, as an escaped dot, slash, parenthesis, underscore or hyphen does. Then it puts a slash in front if there is none. ```text recording=urls simplify_regex(): a regular expression made into an address a person can read simplify_regex('^tickets/(?P[0-9]+)/(?P[0-9]{2})/\\Z') -> '/tickets///' simplify_regex('^plans/(?P[0-9])(?:\\.(?Ppdf|svg))?$') -> '/plans/' simplify_regex('^archive/([0-9]{4})/([0-9]{2})/$') -> '/archive///' simplify_regex('east/rooms//audio//') -> '/east/rooms//audio//' ``` Deleting a group that does not capture deletes whatever is inside it, so the optional format of the museum's plan address is gone from the second line. The fourth is a route, and gains only the slash in front. The command listurls is those two functions and some formatting. It imports the module `ROOT_URLCONF` names and reads the list from it directly, without the resolver. It extracts, simplifies each address, names each view by its module and its name, joins a pattern's namespaces to its name with colons, and prints the rows, sorted unless it is told otherwise (`django/core/management/commands/listurls.py:Command.get_url_patterns`, `django/core/management/commands/listurls.py:Command.handle`). The recording runs it with `call_command`: ```text recording=urls call_command("listurls"), with ROOT_URLCONF = 'museum.urls': each line as printed, without the spaces at its end / museum.views.entrance entrance /east/ museum.views.wing east:wing /east/rooms// museum.views.room east:room /east/rooms//audio// museum.views.track east:audio:track /files/ museum.views.download download /plans/ museum.views.plan plan /shop/ museum.views.shop shop /shop// museum.views.item item /tickets// museum.views.tickets tickets /tickets/// museum.views.tickets tickets /west/ museum.views.wing west:wing /west/rooms// museum.views.room west:room /west/rooms//audio// museum.views.track west:audio:track ``` The names in the last column are the names to reverse with. > **New in 6.2.** The command listurls was added in this release. The admin's documentation pages list a project's views with the same two functions (`django/contrib/admindocs/views.py:ViewIndexView`).