From dd4f04fa56b2f0b1b86413d0bbfdcf40dde11d40 Mon Sep 17 00:00:00 2001
From: gwen <gremond@cadoles.com>
Date: Thu, 4 Jun 2015 10:10:58 +0200
Subject: [PATCH] =?UTF-8?q?ajout=20de=20doc=20sur=20les=20m=C3=A9ta=20clas?=
 =?UTF-8?q?ses?=
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---
 python/formation/classes.txt | 70 ++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)

diff --git a/python/formation/classes.txt b/python/formation/classes.txt
index 085c9d6..1ba2268 100644
--- a/python/formation/classes.txt
+++ b/python/formation/classes.txt
@@ -380,3 +380,73 @@ autre exemple : les méthodes statiques
 ...      # do stuff here
          
          
+métaclasses
+-----------------
+
+>>> class A:
+...   pass
+... 
+>>> type(A)
+<type 'classobj'>
+>>> class B(object): pass
+... 
+>>> type(B)
+<type 'type'>
+>>> help(type)
+
+>>> C = type('C', (), {})
+>>> C
+<class '__main__.C'>
+>>> 
+
+>>> type(object)
+<type 'type'>
+>>> type(type)
+<type 'type'>
+>>> isinstance(type, object)
+True
+>>> isinstance(object, type)
+True
+>>> 
+
+::
+
+  class MaMetaClasse(type):
+    """Exemple d'une métaclasse."""
+    def __new__(metacls, nom, bases, dict):
+        """Création de notre classe."""
+        print("On crée la classe {}".format(nom))
+        return type.__new__(metacls, nom, bases, dict)
+
+  class MaClasse(object):
+    __metaclass__ = MaMetaClasse
+
+
+exemple : forcer l'implémentation d'un singleton avec les métaclasses 
+
+::
+
+  class Singleton(type):
+    instance = None
+    def __call__(cls, *args, **kw):
+        if not cls.instance:
+             cls.instance = super(Singleton, cls).__call__(*args, **kw)
+        return cls.instance
+
+  class ASingleton(object):
+    __metaclass__ = Singleton
+
+    a = ASingleton()
+    b = ASingleton()
+    assert a is b
+    print(a.__class__.__name__, b.__class__.__name__)
+    
+    class BSingleton(object):
+        __metaclass__ = Singleton
+    
+    c = BSingleton()
+    d = BSingleton()
+    assert c is d
+    print(c.__class__.__name__, d.__class__.__name__)
+    assert c is not a
+