meh

betty/service/__init__.py

@@ -13,7 +13,7 @@
 
 
 class CyclicDependency(RuntimeError):
-    def __init__(self, service_ids: Sequence[str]):
+    def __init__(self, service_ids: Sequence[ServiceId]):
         assert len(service_ids) > 1
         traceback = []
         for index, service_id in enumerate(service_ids):
@@ -30,12 +30,19 @@ def __init__(self, service_ids: Sequence[str]):
 ''')
 
 
-class _ServiceNotFound(RuntimeError):
-    pass
+class ServiceNotFound(RuntimeError):
+    def __init__(self, service_id: ServiceId):
+        super().__init__(f'Unknown service "{service_id}".')
 
 
-class _ServiceContainerNotStarted(RuntimeError):
-    pass
+class ServiceContainerNotStarted(RuntimeError):
+    def __init__(self):
+        super().__init__('This service container has not yet started.')
+
+
+class ServiceContainerStarted(RuntimeError):
+    def __init__(self):
+        super().__init__('This service container has already started.')
 
 
 class ServiceContainer:
@@ -46,6 +53,7 @@ class ServiceContainer:
 
     Implementations must be thread-safe.
     """
+
     async def get(self, service_id: ServiceId) -> Service:
         raise NotImplementedError(type(self))
 
@@ -69,6 +77,7 @@ class ServiceContainerBuilder:
 
     A service container builder allows you to define the services to build a service container with.
     """
+
     @overload
     def define(self, service_id: ServiceId, *, service_factory: ServiceFactory) -> None:
         pass

betty/service/_default.py

@@ -5,8 +5,8 @@
 from typing_extensions import override
 
 from betty.concurrent import AsynchronizedLock, _Lock
-from betty.service import ServiceContainer, ServiceId, ServiceFactory, Service, _ServiceNotFound, \
-    ServiceContainerBuilder, CyclicDependency
+from betty.service import ServiceContainer, ServiceId, ServiceFactory, Service, ServiceNotFound, \
+    ServiceContainerBuilder, CyclicDependency, ServiceContainerNotStarted, ServiceContainerStarted
 
 
 class _ServiceContainerBase(ServiceContainer):
@@ -29,16 +29,25 @@ async def _lock(self, service_id: ServiceId) -> _Lock:
         async with self._locks_lock:
             return self._locks[service_id]
 
+    def _assert_started(self) -> None:
+        if not self._started:
+            raise ServiceContainerNotStarted()
+
+    def _assert_not_started(self) -> None:
+        if self._started:
+            raise ServiceContainerStarted()
+
     async def start(self) -> None:
+        self._assert_not_started()
         assert not self._started
         self._started = True
 
     async def stop(self) -> None:
-        assert self._started
+        self._assert_started()
 
     @override
     async def get(self, service_id: ServiceId) -> Service:
-        assert self._started
+        self._assert_started()
         async with await self._lock(service_id):
             try:
                 return self._services[service_id]
@@ -108,7 +117,7 @@ async def _initialize(self, service_id: ServiceId) -> Service:
         try:
             service_factory = self._service_factories[service_id]
         except KeyError:
-            raise _ServiceNotFound(f'Service "{service_id}" is unknown.')
+            raise ServiceNotFound(f'Service "{service_id}" is unknown.')
         service_context = service_factory(self)
         service = await service_context.__aenter__()
         self._entered_service_contexts.append(service_context)

betty/tests/service/test_default.py

@@ -5,7 +5,7 @@
 
 import pytest
 
-from betty.service import _ServiceNotFound, ServiceContainer, CyclicDependency
+from betty.service import ServiceNotFound, ServiceContainer, CyclicDependency
 from betty.service._default import DefaultServiceContainerBuilder
 
 
@@ -36,7 +36,7 @@ async def test_without_services(self) -> None:
     async def test_with_unknown_service(self) -> None:
         builder = DefaultServiceContainerBuilder()
         async with builder.build() as services:
-            with pytest.raises(_ServiceNotFound):
+            with pytest.raises(ServiceNotFound):
                 await services.get('UnknownServiceId')
 
     async def test_with_as_is_service(self) -> None: