Display missing route details.

starlette/routing.py

@@ -31,6 +31,10 @@ class NoMatchFound(Exception):
  if no matching route exists.
  """
 
+ def __init__(self, name: str, path_params: typing.Dict[str, typing.Any]) -> None:
+ params = ", ".join(list(path_params.keys()))
+ super().__init__(f'No route exists for name "{name}" and params "{params}".')
+
 
 class Match(Enum):
  NONE = 0
@@ -240,7 +244,7 @@ def url_path_for(self, name: str, **path_params: typing.Any) -> URLPath:
  expected_params = set(self.param_convertors.keys())
 
  if name != self.name or seen_params != expected_params:
- raise NoMatchFound()
+ raise NoMatchFound(name, path_params)
 
  path, remaining_params = replace_params(
  self.path_format, self.param_convertors, path_params
@@ -309,7 +313,7 @@ def url_path_for(self, name: str, **path_params: typing.Any) -> URLPath:
  expected_params = set(self.param_convertors.keys())
 
  if name != self.name or seen_params != expected_params:
- raise NoMatchFound()
+ raise NoMatchFound(name, path_params)
 
  path, remaining_params = replace_params(
  self.path_format, self.param_convertors, path_params
@@ -408,7 +412,7 @@ def url_path_for(self, name: str, **path_params: typing.Any) -> URLPath:
  )
  except NoMatchFound:
  pass
- raise NoMatchFound()
+ raise NoMatchFound(name, path_params)
 
  async def handle(self, scope: Scope, receive: Receive, send: Send) -> None:
  await self.app(scope, receive, send)
@@ -472,7 +476,7 @@ def url_path_for(self, name: str, **path_params: typing.Any) -> URLPath:
  return URLPath(path=str(url), protocol=url.protocol, host=host)
  except NoMatchFound:
  pass
- raise NoMatchFound()
+ raise NoMatchFound(name, path_params)
 
  async def handle(self, scope: Scope, receive: Receive, send: Send) -> None:
  await self.app(scope, receive, send)
@@ -593,7 +597,7 @@ def url_path_for(self, name: str, **path_params: typing.Any) -> URLPath:
  return route.url_path_for(name, **path_params)
  except NoMatchFound:
  pass
- raise NoMatchFound()
+ raise NoMatchFound(name, path_params)
 
  async def startup(self) -> None:
  """

tests/test_routing.py

@@ -243,8 +243,14 @@ def test_url_path_for():
  assert app.url_path_for("homepage") == "/"
  assert app.url_path_for("user", username="tomchristie") == "/users/tomchristie"
  assert app.url_path_for("websocket_endpoint") == "/ws"
- with pytest.raises(NoMatchFound):
+ with pytest.raises(
+ NoMatchFound, match='No route exists for name "broken" and params "".'
+ ):
  assert app.url_path_for("broken")
+ with pytest.raises(
+ NoMatchFound, match='No route exists for name "broken" and params "key, key2".'
+ ):
+ assert app.url_path_for("broken", key="value", key2="value2")
  with pytest.raises(AssertionError):
  app.url_path_for("user", username="tom/christie")
  with pytest.raises(AssertionError):