Improve resource subclasses typing and make shutdown definition optional (#492)

* Improve resource subclasses typing and make shutdown definition optional

* Update mypy tests

Author: rmk135

src/dependency_injector/resources.py

@@ -1,7 +1,7 @@
 """Resources module."""
 
 import abc
-from typing import TypeVar, Generic
+from typing import TypeVar, Generic, Optional
 
 
 T = TypeVar('T')
@@ -10,20 +10,18 @@
 class Resource(Generic[T], metaclass=abc.ABCMeta):
 
     @abc.abstractmethod
-    def init(self, *args, **kwargs) -> T:
+    def init(self, *args, **kwargs) -> Optional[T]:
         ...
 
-    @abc.abstractmethod
-    def shutdown(self, resource: T) -> None:
+    def shutdown(self, resource: Optional[T]) -> None:
         ...
 
 
 class AsyncResource(Generic[T], metaclass=abc.ABCMeta):
 
     @abc.abstractmethod
-    async def init(self, *args, **kwargs) -> T:
+    async def init(self, *args, **kwargs) -> Optional[T]:
         ...
 
-    @abc.abstractmethod
-    async def shutdown(self, resource: T) -> None:
+    async def shutdown(self, resource: Optional[T]) -> None:
         ...

tests/typing/resource.py

@@ -1,4 +1,4 @@
-from typing import List, Iterator, Generator, AsyncIterator, AsyncGenerator
+from typing import List, Iterator, Generator, AsyncIterator, AsyncGenerator, Optional
 
 from dependency_injector import providers, resources
 
@@ -35,7 +35,7 @@ class MyResource4(resources.Resource[List[int]]):
     def init(self, *args, **kwargs) -> List[int]:
         return []
 
-    def shutdown(self, resource: List[int]) -> None:
+    def shutdown(self, resource: Optional[List[int]]) -> None:
         ...
 
 
@@ -87,7 +87,7 @@ class MyResource8(resources.AsyncResource[List[int]]):
     async def init(self, *args, **kwargs) -> List[int]:
         return []
 
-    async def shutdown(self, resource: List[int]) -> None:
+    async def shutdown(self, resource: Optional[List[int]]) -> None:
         ...
 
 

tests/unit/providers/test_resource_py35.py

@@ -1,6 +1,7 @@
 """Dependency injector resource provider unit tests."""
 
 import asyncio
+import inspect
 import unittest
 from typing import Any
 
@@ -158,27 +159,21 @@ def shutdown(self, resource: TestDependency) -> None: ...
 
         self.assertTrue(issubclass(TestResource, resources.Resource))
 
-    def test_init_class_abc_definition_is_required(self):
+    def test_init_class_abc_init_definition_is_required(self):
         class TestResource(resources.Resource):
             ...
 
         with self.assertRaises(TypeError) as context:
             TestResource()
 
         self.assertIn("Can't instantiate abstract class TestResource", str(context.exception))
-        self.assertIn("init, shutdown", str(context.exception))
+        self.assertIn("init", str(context.exception))
 
-
-    def test_init_class_abc_shutdown_definition_is_required(self):
+    def test_init_class_abc_shutdown_definition_is_not_required(self):
         class TestResource(resources.Resource):
             def init(self):
                 ...
-
-        with self.assertRaises(TypeError) as context:
-            TestResource()
-
-        self.assertIn("Can't instantiate abstract class TestResource", str(context.exception))
-        self.assertIn("shutdown", str(context.exception))
+        self.assertTrue(hasattr(TestResource(), 'shutdown'))
 
     def test_init_not_callable(self):
         provider = providers.Resource(1)
@@ -497,26 +492,22 @@ async def shutdown(self, resource: TestDependency) -> None: ...
 
         self.assertTrue(issubclass(TestAsyncResource, resources.AsyncResource))
 
-    def test_init_async_class_abc_definition_is_required(self):
+    def test_init_async_class_abc_init_definition_is_required(self):
         class TestAsyncResource(resources.AsyncResource):
             ...
 
         with self.assertRaises(TypeError) as context:
             TestAsyncResource()
 
         self.assertIn("Can't instantiate abstract class TestAsyncResource", str(context.exception))
-        self.assertIn("init, shutdown", str(context.exception))
+        self.assertIn("init", str(context.exception))
 
-    def test_init_async_class_abc_shutdown_definition_is_required(self):
+    def test_init_async_class_abc_shutdown_definition_is_not_required(self):
         class TestAsyncResource(resources.AsyncResource):
             async def init(self):
                 ...
-
-        with self.assertRaises(TypeError) as context:
-            TestAsyncResource()
-
-        self.assertIn("Can't instantiate abstract class TestAsyncResource", str(context.exception))
-        self.assertIn("shutdown", str(context.exception))
+        self.assertTrue(hasattr(TestAsyncResource(), 'shutdown'))
+        self.assertTrue(inspect.iscoroutinefunction(TestAsyncResource.shutdown))
 
     def test_init_with_error(self):
         async def _init():