[Dev OpenGP] [14] Created Metaclass

[subversion@xxxxxxxxxxxxx]

Revision: 14
Author:   alband85
Date:     2009-02-08 00:44:47 +0100 (Sun, 08 Feb 2009)

Log Message:
-----------
Created Metaclass

Added Paths:
-----------
    trunk/src/Metaclass.py


Added: trunk/src/Metaclass.py
===================================================================
--- trunk/src/Metaclass.py	                        (rev 0)
+++ trunk/src/Metaclass.py	2009-02-07 23:44:47 UTC (rev 14)
@@ -0,0 +1,49 @@
+# For more informations, see http://code.activestate.com/recipes/266468/
+
+class Metaclass (type):
+	
+	def __init__(cls, name, bases, *args, **kwargs):
+		"""Configure a new class
+
+		@param cls: Class object
+		@param name: Name of the class
+		@param bases: All base classes for cls
+		"""
+		super(Metaclass, cls).__init__(cls, name, bases, *args, **kwargs)
+
+		# Detach cls.new() from class Metaclass, and make it a method
+		# of cls.
+		cls.__new__ = staticmethod(cls.new)
+
+		# Find all abstract methods, and assign the resulting list to
+		# cls.__abstractmethods__, so we can read that variable when a
+		# request for allocation (__new__) is done.
+		abstractmethods = []
+		ancestors = list(cls.__mro__)
+		ancestors.reverse()  # Start with __builtin__.object
+		for ancestor in ancestors:
+			for clsname, clst in ancestor.__dict__.items():
+				if isinstance(clst, AbstractMethod):
+					abstractmethods.append(clsname)
+				else:
+					if clsname in abstractmethods:
+						abstractmethods.remove(clsname)
+
+		abstractmethods.sort()
+		setattr(cls, '__abstractmethods__', abstractmethods)
+
+	def new(self, cls):
+		"""Allocator for class cls
+
+		@param self: Class object for which an instance should be
+			created.
+
+		@param cls: Same as self.
+		"""
+		if len(cls.__abstractmethods__):
+			raise NotImplementedError('Can\'t instantiate class `' + \
+									  cls.__name__ + '\';\n' + \
+									  'Abstract methods: ' + \
+									  ", ".join(cls.__abstractmethods__))
+
+		return object.__new__(self)