Update What Is DI docs and example

docs/main/introduction/what_is_di.rst

@@ -74,25 +74,26 @@ Example
 
 Let's go through the code of ``example.py``:
 
-.. literalinclude:: ../../../examples/di_demo/example.py
+.. literalinclude:: ../../../examples/ioc_di_demos/example.py
    :language: python
 
 At some point, things defined above mean, that the code from ``example.py``, 
 could look different, like in ``ioc_example.py``:
 
-.. literalinclude:: ../../../examples/di_demo/ioc_example.py
+.. literalinclude:: ../../../examples/ioc_di_demos/ioc_example.py
    :language: python
 
-Also the code from ``ioc_example.py`` could be powered by dependency 
-injection framework, like in ``di_example.py``:
+Also the code from ``ioc_example.py`` could be upgraded with inversion of 
+control container, like in ``ioc_container_example.py``:
 
-.. literalinclude:: ../../../examples/di_demo/di_example.py
+.. literalinclude:: ../../../examples/ioc_di_demos/ioc_container_example.py
    :language: python
     
 .. note::
 
-    ``Components`` from ``di_example.py`` is an IoC container. It contains a 
-    collection of component providers that could be injected into each other. 
+    ``Components`` from ``ioc_container_example.py`` is an IoC container. It 
+    contains a collection of component providers that could be injected into 
+    each other. 
 
     Assuming this, ``Components`` could be one and the only place, where 
     application's structure is being managed on the high level.

examples/ioc_di_demos/car_engine_1.py

@@ -0,0 +1,18 @@
+"""Car & Engine example 1."""
+
+
+class Engine(object):
+    """Example engine."""
+
+
+class Car(object):
+    """Example car."""
+
+    def __init__(self):
+        """Initializer."""
+        self.engine = Engine()
+
+
+if __name__ == '__main__':
+    car = Car()
+    assert car.engine is not None

examples/ioc_di_demos/car_engine_2.py

@@ -0,0 +1,18 @@
+"""Car & Engine example 2."""
+
+
+class Engine(object):
+    """Example engine."""
+
+
+class Car(object):
+    """Example car."""
+
+    def __init__(self, engine):
+        """Initializer."""
+        self.engine = engine
+
+
+if __name__ == '__main__':
+    car = Car(Engine())
+    assert car.engine is not None

examples/ioc_di_demos/ioc_container_example.py

@@ -1,7 +1,10 @@
-"""The Code, powered by Dependency Injector."""
+"""The Code, that uses IoC container."""
 
-from dependency_injector import catalogs, providers
-from ioc_example import Service, Client
+from dependency_injector import catalogs
+from dependency_injector import providers
+
+from ioc_example import Service
+from ioc_example import Client
 
 
 class Components(catalogs.DeclarativeCatalog):