Add docs

docs/providers/configuration.rst

@@ -143,6 +143,28 @@ With the ``.as_(callback, *args, **kwargs)`` you can specify a function that wil
 before the injection. The value from the config will be passed as a first argument. The returned
 value will be injected. Parameters ``*args`` and ``**kwargs`` are handled as any other injections.
 
+Strict mode and required options
+--------------------------------
+
+You can use configuration provider in strict mode. In strict mode configuration provider raises an error
+on access to any undefined option.
+
+.. literalinclude:: ../../examples/providers/configuration/configuration_strict.py
+   :language: python
+   :lines: 3-
+   :emphasize-lines: 12
+
+You can also use ``.required()`` option modifier when making an injection.
+
+.. literalinclude:: ../../examples/providers/configuration/configuration_required.py
+   :language: python
+   :lines: 11-20
+   :emphasize-lines: 8-9
+
+.. note::
+
+   Modifier ``.required()`` should be specified before type modifier ``.as_*()``.
+
 Injecting invariants
 --------------------
 

examples/providers/configuration/configuration_required.py

@@ -0,0 +1,30 @@
+"""`Configuration` provider strict mode example."""
+
+from dependency_injector import containers, providers, errors
+
+
+class ApiClient:
+    def __init__(self, api_key: str, timeout: int):
+        self.api_key = api_key
+        self.timeout = timeout
+
+
+class Container(containers.DeclarativeContainer):
+
+    config = providers.Configuration()
+
+    api_client_factory = providers.Factory(
+        ApiClient,
+        api_key=config.api.key.required(),
+        timeout=config.api.timeout.required().as_int(),
+    )
+
+
+if __name__ == '__main__':
+    container = Container()
+
+    try:
+        api_client = container.api_client_factory()
+    except errors.Error:
+        # raises error: Undefined configuration option "config.api.key"
+        ...

examples/providers/configuration/configuration_strict.py

@@ -0,0 +1,30 @@
+"""`Configuration` provider strict mode example."""
+
+from dependency_injector import containers, providers, errors
+
+
+class ApiClient:
+    def __init__(self, api_key: str, timeout: int):
+        self.api_key = api_key
+        self.timeout = timeout
+
+
+class Container(containers.DeclarativeContainer):
+
+    config = providers.Configuration(strict=True)
+
+    api_client_factory = providers.Factory(
+        ApiClient,
+        api_key=config.api.key,
+        timeout=config.api.timeout.as_int(),
+    )
+
+
+if __name__ == '__main__':
+    container = Container()
+
+    try:
+        api_client = container.api_client_factory()
+    except errors.Error:
+        # raises error: Undefined configuration option "config.api.key"
+        ...