Added documentation section explaining how to use Callable provider in a reusable, configurable approach

Author: Tomasz Borczyk

docs/providers/callable.rst

@@ -14,6 +14,15 @@ Callable provider
    :language: python
    :lines: 3-
 
+
+If you would like to inject :py:class:`Callable` instance to a service using :py:class:`Provide` and the wiring
+mechanism, then you should use the ``.provider`` field. This way :py:class:`Callable` instance will not be called
+when being provided, and the service can deliver their own additional arguments.
+
+.. literalinclude:: ../../examples/providers/callable_reusable.py
+   :language: python
+   :lines: 3-
+
 ``Callable`` provider handles an injection of the dependencies the same way like a
 :ref:`factory-provider`.
 

examples/providers/callable_reusable.py

@@ -0,0 +1,38 @@
+"""`Callable` provider example with configurable parameters"""
+
+import passlib.hash
+
+from dependency_injector import containers, providers
+from dependency_injector.wiring import Provide
+
+
+class Service:
+    def __init__(self, hasher):
+        self.hasher = hasher
+
+    def hash(self, value):
+        return self.hasher(value)
+
+
+class Container(containers.DeclarativeContainer):
+
+    password_hasher = providers.Callable(
+        passlib.hash.sha256_crypt.hash,
+        salt_size=16,
+        rounds=10000,
+    )
+    password_verifier = providers.Callable(passlib.hash.sha256_crypt.verify)
+
+    service = providers.Factory(
+        Service,
+        hasher=password_hasher.provider
+    )
+
+
+if __name__ == "__main__":
+    service: Service = Provide["service"]
+    container = Container()
+    container.wire(modules=[__name__])
+
+    hashed_password = service.hash("super secret")
+    assert container.password_verifier("super secret", hashed_password)