Ticket #5985: trac_5985_test_class_pickling.patch

new file sage/misc/test_class_pickling.py

@@ +1 @@
+from sage.misc.cachefunc import cached_function
+
+class bar:
+    pass
+
+def metaclass(name, bases):
+    """
+    Creates a new class in this metaclass
+
+    INPUT::
+     - name: a string
+     - bases: a tuple of classes
+
+    EXAMPLES::
+
+        sage: from sage.misc.test_class_pickling import metaclass, bar
+        sage: c = metaclass("foo2", (object, bar,))
+        constructing class
+        sage: c
+        <class 'sage.misc.test_class_pickling.foo2'>
+        sage: type(c)
+        <class 'sage.misc.test_class_pickling.Metaclass'>
+        sage: c.__bases__
+        (<type 'object'>, <class sage.misc.test_class_pickling.bar at ...>)
+
+    """
+    print "constructing class"
+    result = Metaclass(name, bases, dict())
+    result.reduce_args = (name, bases)
+    return result
+
+class Metaclass(type):
+    """
+    This metaclass illustrates the customization of how a class is pickled.
+    It requires a slightly patched version of cPickle.
+
+    See:
+     - http://docs.python.org/library/copy_reg.html#module-copy_reg
+     - http://groups.google.com/group/comp.lang.python/browse_thread/thread/66c282afc04aa39c/
+     - http://groups.google.com/group/sage-devel/browse_thread/thread/583048dc7d373d6a/
+
+    EXAMPLES::
+
+        sage: from sage.misc.test_class_pickling import metaclass, bar
+        sage: c = metaclass("foo", (object, bar,))
+        constructing class
+        sage: import cPickle
+        sage: s = cPickle.dumps(c)
+        reducing a class
+        sage: c2 = cPickle.loads(s)
+        constructing class
+        sage: c = c2 = 1
+
+    """
+    def __reduce__(self):
+        """
+        Implements the pickle protocol for classes in this metaclass
+        (not for the instances of this class!!!)
+
+        EXAMPLES::
+
+            sage: from sage.misc.test_class_pickling import metaclass, bar
+            sage: c = metaclass("foo3", (object, bar,))
+            constructing class
+            sage: c.__class__.__reduce__(c)
+            reducing a class
+            (<function metaclass at ...>, ('foo3', (<type 'object'>, <class sage.misc.test_class_pickling.bar at ...>)))
+        """
+        print "reducing a class"
+        return (metaclass, self.reduce_args)
+
+
+import copy_reg
+copy_reg.pickle(Metaclass, Metaclass.__reduce__)