Intro_to_Solid.md

@@ -177,9 +177,162 @@ That will be more simple to do extension.
 This convention tells us to create a substitutable subclass for their parents.
 So, if you want to create an object in the subclass, you have to be able to pass it in the interface.
 
+Let's make an example !
+We will write a _Walk_ class and his subclass, _Jump_ class.
+```python
+class Walk(abc.ABC):
+    def __init__(self):
+        abc.ABC.__init__(self)
+    @abc.abstractmethod
+    def Speed(self):
+        pass
+    @abc.abstractmethod
+    def Ahead(self):
+        pass
+        '''the player walk ahead'''
+
+    @abc.abstractmethod
+    def Behind(self):
+        pass
+    '''the player walk behind'''
+```
+And the _Jump_ subclass.
+```python
+class Jump(Walk):
+    def __init__(self):
+        pass
+
+    def Speed(self):
+        pass
+
+    def Ahead(self):
+        pass
+
+    def Behind(self):
+        pass
+```
+As you can see, the _Jump_ subclass has all abstract method of _Walk_ class.
+But we have a big problem !
+The _Jump_ subclass need a new method, the _height_ method.
+And he does not need the _Ahead_ and _Behind_ method.
+If you remove abstract method and add a new method in _Jump_ subclass, you will be in a big trouble.
+This subclass will be different about mother class.
+The simple way to resolve this trouble is to create a new mother class for _Walk_ and _Jump_ class.
+
+```python
+class Movement(abc.ABC):
+    def __init__(self):
+        abc.ABC.__init__(self)
+        
+    @abc.abstractmethod
+    def Speed(self):
+        pass
+    
+    @abc.abstractmethod
+    def Animation(self):
+        pass
+    
+    @abc.abstractmethod
+    def Direction(self):
+        pass
+```
+The _Movement_ class will be the mother class of _Walk_ and _Jump_ classes.
+These subclasses will have three methods (_Speed_, _Animation_ and _Direction_ methods).
+The problems that we had is resolved with the _Direction_ method.
+With this method, you have choices to go ahead, behind, height, etc. 
+
+<details>
+<summary>
+Subclasses
+</summary>
+The _Walk_ subclass:
+
+```python
+class Walk(Movement):
+    def __init__(self):
+        pass
+
+    def Speed(self):
+        pass
+
+    def Animation(self):
+        pass
+
+
+    def Direction(self):
+        pass
+
+```
+And the _Jump_ subclass:
+
+```python
+class Jump(Movement):
+    def __init__(self):
+        pass
+    def Speed(self):
+        pass
+
+    def Animation(self):
+        pass
+
+    def Direction(self):
+        pass
+
+```
+
+</details>
+
 ### Interface Segregation Principle
 
 The _Interface Segregation Principle_ means that all interfaces have to be separated.
 That means that clients has not functions that they do not need.
 
+OK ! So, let's make an example with client manager.
+
+```python
+class GoodCustomer(abc.ABC):
+    def __init__(self):
+        abc.ABC.__init__(self)
+        
+    @abc.abstractmethod
+    def FirstName(self):
+        pass
+    @abc.abstractmethod
+    def LastName(self):
+        pass
+    @abc.abstractmethod
+    def Address(self):
+        pass
+    
+    @abc.abstractmethod
+    def Work(self):
+        pass
+```
+The _GoodCustomer_ mother class is a class where good customer information are saved.
+
+```python 
+class BadCustomer(GoodCustomer):
+    def __init__(self):
+        pass
+
+    def FirstName(self):
+        pass
+
+    def LastName(self):
+        pass
+
+    def Address(self):
+        pass
+
+    def Work(self):
+        pass
+```
+The _BadCustomer_ subclass is a class where bad customer information are saved.
+For this example, we don't want to know the addresses of bad guys. 
+So what can we do ?
+
+You have to create a new mother class for these two classes like the preceding example.
 ### Dependency Inversion Principle
+
+This convention says that all classes that we use depends on the interface or abstract classes.
+Like precedents example, all methods was abstracts.