Calling "url_for" in a Jinja2 template results in NoMatchFound

[EntangledLabs]

I am writing a web app in Starlette using Jinja2 templates. While writing a custom token auth system, I stumbled across a NoMatchFound error.

So, I tried to figure out why exactly it isn't working. In a lifespan manager, I printed out each route and its associated url_path_for like so:

@asynccontextmanager
async def lifespan(app):
    for route in app.router.routes:
        print(route)
        if isinstance(route, Mount):
            if isinstance(route.app, Router):
                for mount_route in route.app.routes:
                    print(mount_route)
                    print(mount_route.url_path_for(mount_route.name))
        else:
            print(route.url_path_for(route.name))

The following is the output:

Route(path='/', name='index', methods=['GET', 'HEAD'])
/
Route(path='/login', name='login', methods=['GET', 'HEAD'])
/login
Route(path='/logout', name='logout', methods=['GET', 'HEAD'])
/logout
Route(path='/token', name='get_token', methods=['POST'])
/token
Mount(path='/admin', name='', app=<starlette.routing.Router object at 0x000002CB2403E520>)
Mount(path='/user', name='', app=<starlette.routing.Router object at 0x000002CB24138640>)
Mount(path='/static', name='static', app=<starlette.staticfiles.StaticFiles object at 0x000002CB240396A0>)

So far, so good.

I then called url_path_for another time, except directly on the app's router object:

print(app.router.url_path_for('token'))

This is the resulting stack trace:

ERROR:    Traceback (most recent call last):
  File ".venv\Lib\site-packages\starlette\routing.py", line 693, in lifespan
    async with self.lifespan_context(app) as maybe_state:
               ~~~~~~~~~~~~~~~~~~~~~^^^^^
  File "Python\Python313\Lib\contextlib.py", line 214, in __aenter__
    return await anext(self.gen)
           ^^^^^^^^^^^^^^^^^^^^^
  File "<project root>\main\webapp\main.py", line 30, in lifespan
    print(app.router.url_path_for('token'))
          ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^
  File ".venv\Lib\site-packages\starlette\routing.py", line 662, in url_path_for
    raise NoMatchFound(name, path_params)
starlette.routing.NoMatchFound: No route exists for name "token" and params "".

As far as I can tell, I should be getting the appropriate path. Is there something I'm doing wrong here? Or is this an issue with Starlete?

[Kludex]

The name is 'get_token', not 'token'.

[Kludex]

An endpoint has the default name as the name of the function. But you can change that on the Route.

But yes, it's always the name. As you can see on the error message.

[EntangledLabs]

Gotcha, thanks for the clarification. Is it possible to update the documentation to include this? the current information about url_for is extremely sparse

[Kludex]

Can you point me to the places you find unclear? I think there are two places that mention this function. I'm away from the computer.

[EntangledLabs]

I'm only familiar with the mention on the Templates page (https://www.starlette.io/templates/), which states the following:

The Jinja2 template context will automatically include a url_for function, so we can correctly hyperlink to other pages within the application.

Not necessarily that it's unclear but that it's somewhat ambiguous as to how it's meant to be used

[EntangledLabs]

Perhaps something like url_for will search for the route by its name, which by default will be the name of the endpoint specified