Merge pull request #31 from pro1code1hack/10_Mixin

10 mixin

Author: pro1code1hack

Object_Oriented_Programming/10_Mixin.md

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+# Mixin
+
+_A class that offers method implementations for reuse by several connected child classes is
+known as a mixin. The inheritance does not, however, establish a connection._
+
+_A mixin collects a group of techniques for reuse. Each mixin should implement a single
+distinct behavior using techniques that are closely related._
+
+_Mixin classes should be named with the suffix Mixin because Python does not specify a formal way to define them._
+
++ Example:
+
+```python
+class Graphic:
+    def __init__(self, pos_x, pos_y, size_x, size_y):
+        self.pos_x = pos_x
+        self.pos_y = pos_y
+        self.size_x = size_x
+        self.size_y = size_y
+
+
+class Mixin:
+    def resize(self, size_x, size_y):
+        self.size_x = size_x
+        self.size_y = size_y
+
+
+class ResizableClass(Mixin, Graphic):
+    pass
+
+
+rge = ResizableGraphicalEntity(6, 2, 20, 30)
+rge.resize(200, 300)
+```
+
+_Here, the class Mixin derives straight from object rather than Graphic,
+therefore ResizableClass just receives the resize function from it._
+
+_As we previously stated, this makes the ResizableClass
+inheritance tree simpler and lowers the danger of the diamond problem._
+
+_It frees us from having to inherit undesirable methods when using Graphic
+as a parent for other types._
+
+_Tips:_
+
++ Simple class modifications are added using mixin classes.
++ Python uses multiple inheritance to implement mixins, which have a powerful expressive capacity but call for careful
+  design.