Optionally allow overriding of dependencies

CHANGES.md

@@ -1,6 +1,9 @@
 python-inject changes
 =====================
 
+### 5.0.1 (2023-10-16)
+- Optionally allow overriding dependencies.
+
 ### 5.0.0 (2023-06-10)
 - Support for PEP0604 for Python>=3.10.
 

README.md

@@ -100,7 +100,6 @@ class User(object):
 
 # Create an optional configuration.
 def my_config(binder):
-    binder.install(my_config2)  # Add bindings from another config.
     binder.bind(Cache, RedisCache('localhost:1234'))
 
 # Configure a shared injector.
@@ -133,13 +132,33 @@ and optionally `inject.clear()` to clean up on tear down:
 class MyTest(unittest.TestCase):
     def setUp(self):
         inject.clear_and_configure(lambda binder: binder
-            .bind(Cache, Mock()) \
+            .bind(Cache, MockCache()) \
             .bind(Validator, TestValidator()))
 
     def tearDown(self):
         inject.clear()
 ```
 
+## Composable configurations
+You can reuse configurations and override already registered dependencies to fit the needs in different environments or specific tests.
+```python
+    def base_config(binder):
+        # ... more dependencies registered here
+        binder.bind(Validator, RealValidator())
+        binder.bind(Cache, RedisCache('localhost:1234'))
+
+    def tests_config(binder):
+        # reuse existing configuration
+        binder.install(base_config)
+
+        # override only certain dependencies
+        binder.bind(Validator, TestValidator())
+        binder.bind(Cache, MockCache())
+
+    inject.clear_and_configure(tests_config, allow_override=True)
+
+```
+
 ## Thread-safety
 After configuration the injector is thread-safe and can be safely reused by multiple threads.
 

src/inject/__init__.py

@@ -122,8 +122,9 @@ def __init__(self, constructor: Callable, previous_error: TypeError):
 class Binder(object):
     _bindings: Dict[Binding, Constructor]
 
-    def __init__(self) -> None:
+    def __init__(self, allow_override: bool = False) -> None:
         self._bindings = {}
+        self.allow_override = allow_override
 
     def install(self, config: BinderCallable) -> 'Binder':
         """Install another callable configuration."""
@@ -171,7 +172,7 @@ def _check_class(self, cls: Binding) -> None:
         if cls is None:
             raise InjectorException('Binding key cannot be None')
 
-        if cls in self._bindings:
+        if not self.allow_override and cls in self._bindings:
             raise InjectorException('Duplicate binding, key=%s' % cls)
 
         if self._is_forward_str(cls):
@@ -197,10 +198,12 @@ def _is_forward_str(self, cls: Binding) -> bool:
 class Injector(object):
     _bindings: Dict[Binding, Constructor]
 
-    def __init__(self, config: Optional[BinderCallable] = None, bind_in_runtime: bool = True):
+    def __init__(
+        self, config: Optional[BinderCallable] = None, bind_in_runtime: bool = True, allow_override: bool = False
+    ):
         self._bind_in_runtime = bind_in_runtime
         if config:
-            binder = Binder()
+            binder = Binder(allow_override)
             config(binder)
             self._bindings = binder._bindings
         else:
@@ -358,33 +361,39 @@ def injection_wrapper(*args: Any, **kwargs: Any) -> T:
         return injection_wrapper
 
 
-def configure(config: Optional[BinderCallable] = None, bind_in_runtime: bool = True) -> Injector:
+def configure(
+    config: Optional[BinderCallable] = None, bind_in_runtime: bool = True, allow_override: bool = False
+) -> Injector:
     """Create an injector with a callable config or raise an exception when already configured."""
     global _INJECTOR
 
     with _INJECTOR_LOCK:
         if _INJECTOR:
             raise InjectorException('Injector is already configured')
 
-        _INJECTOR = Injector(config, bind_in_runtime=bind_in_runtime)
+        _INJECTOR = Injector(config, bind_in_runtime=bind_in_runtime, allow_override=allow_override)
         logger.debug('Created and configured an injector, config=%s', config)
         return _INJECTOR
 
 
-def configure_once(config: Optional[BinderCallable] = None, bind_in_runtime: bool = True) -> Injector:
+def configure_once(
+    config: Optional[BinderCallable] = None, bind_in_runtime: bool = True, allow_override: bool = False
+) -> Injector:
     """Create an injector with a callable config if not present, otherwise, do nothing."""
     with _INJECTOR_LOCK:
         if _INJECTOR:
             return _INJECTOR
 
-        return configure(config, bind_in_runtime=bind_in_runtime)
+        return configure(config, bind_in_runtime=bind_in_runtime, allow_override=allow_override)
 
 
-def clear_and_configure(config: Optional[BinderCallable] = None, bind_in_runtime: bool = True) -> Injector:
+def clear_and_configure(
+    config: Optional[BinderCallable] = None, bind_in_runtime: bool = True, allow_override: bool = False
+) -> Injector:
     """Clear an existing injector and create another one with a callable config."""
     with _INJECTOR_LOCK:
         clear()
-        return configure(config, bind_in_runtime=bind_in_runtime)
+        return configure(config, bind_in_runtime=bind_in_runtime, allow_override=allow_override)
 
 
 def is_configured() -> bool:

test/test_binder.py

@@ -13,15 +13,19 @@ def test_bind(self):
     def test_bind__class_required(self):
         binder = Binder()
 
-        self.assertRaisesRegex(InjectorException, 'Binding key cannot be None',
-                                binder.bind, None, None)
+        self.assertRaisesRegex(InjectorException, 'Binding key cannot be None', binder.bind, None, None)
 
     def test_bind__duplicate_binding(self):
         binder = Binder()
         binder.bind(int, 123)
 
-        self.assertRaisesRegex(InjectorException, "Duplicate binding",
-                                binder.bind, int, 456)
+        self.assertRaisesRegex(InjectorException, "Duplicate binding", binder.bind, int, 456)
+
+    def test_bind__allow_override(self):
+        binder = Binder(allow_override=True)
+        binder.bind(int, 123)
+        binder.bind(int, 456)
+        assert int in binder._bindings
 
     def test_bind_provider(self):
         provider = lambda: 123
@@ -32,8 +36,7 @@ def test_bind_provider(self):
 
     def test_bind_provider__provider_required(self):
         binder = Binder()
-        self.assertRaisesRegex(InjectorException, "Provider cannot be None",
-                                binder.bind_to_provider, int, None)
+        self.assertRaisesRegex(InjectorException, "Provider cannot be None", binder.bind_to_provider, int, None)
 
     def test_bind_constructor(self):
         constructor = lambda: 123
@@ -44,5 +47,4 @@ def test_bind_constructor(self):
 
     def test_bind_constructor__constructor_required(self):
         binder = Binder()
-        self.assertRaisesRegex(InjectorException, "Constructor cannot be None",
-                                binder.bind_to_constructor, int, None)
+        self.assertRaisesRegex(InjectorException, "Constructor cannot be None", binder.bind_to_constructor, int, None)

test/test_inject_configuration.py

@@ -4,7 +4,6 @@
 
 
 class TestInjectConfiguration(BaseTestInject):
-
     def test_configure__should_create_injector(self):
         injector0 = inject.configure()
         injector1 = inject.get_injector()
@@ -19,8 +18,7 @@ def test_configure__should_add_bindings(self):
     def test_configure__already_configured(self):
         inject.configure()
 
-        self.assertRaisesRegex(InjectorException, 'Injector is already configured',
-                                inject.configure)
+        self.assertRaisesRegex(InjectorException, 'Injector is already configured', inject.configure)
 
     def test_configure_once__should_create_injector(self):
         injector = inject.configure_once()
@@ -48,11 +46,19 @@ def test_clear_and_configure(self):
         assert injector1 is not injector0
 
     def test_get_injector_or_die(self):
-        self.assertRaisesRegex(InjectorException, 'No injector is configured',
-                                inject.get_injector_or_die)
+        self.assertRaisesRegex(InjectorException, 'No injector is configured', inject.get_injector_or_die)
 
     def test_configure__runtime_binding_disabled(self):
         injector = inject.configure(bind_in_runtime=False)
-        self.assertRaisesRegex(InjectorException,
-                                "No binding was found for key=<.* 'int'>",
-                                injector.get_instance, int)
+        self.assertRaisesRegex(InjectorException, "No binding was found for key=<.* 'int'>", injector.get_instance, int)
+
+    def test_configure__install_allow_override(self):
+        def base_config(binder):
+            binder.bind(int, 123)
+
+        def config(binder):
+            binder.install(base_config)
+            binder.bind(int, 456)
+
+        injector = inject.configure(config, allow_override=True)
+        assert injector.get_instance(int) == 456