a handy @classproperty decorator

2 files changed, 32 insertions, 0 deletions

diff --git a/lib/sqlalchemy/util.py b/lib/sqlalchemy/util.py
index 873243de1..97270004b 100644
--- a/lib/sqlalchemy/util.py
+++ b/lib/sqlalchemy/util.py
@@ -1639,3 +1639,13 @@ def _decorate_with_warning(func, wtype, message, docstring_header=None):
     decorated = warned(func)
     decorated.__doc__ = doc
     return decorated
+
+class classproperty(property):
+    """A decorator that behaves like @property except that operates
+    on classes rather than instances.
+
+    This is helpful when you need to compute __table_args__ and/or
+    __mapper_args__ when using declarative."""
+    def __get__(desc, self, cls):
+        return desc.fget(cls)
+
diff --git a/test/base/test_utils.py b/test/base/test_utils.py
index e7e4116f7..035e4f268 100644
--- a/test/base/test_utils.py
+++ b/test/base/test_utils.py
@@ -980,3 +980,25 @@ class TestClassHierarchy(TestBase):
         eq_(set(util.class_hierarchy(A)), set((A, B, object)))
     # end Py2K
         
+
+class TestClassProperty(TestBase):
+
+    def test_simple(self):
+
+        from sqlalchemy.util import classproperty
+
+        class A(object):
+            something = {'foo':1}
+
+        class B(A):
+
+            @classproperty
+            def something(cls):
+                d = dict(super(B,cls).something)
+                d.update({'bazz':2})
+                return d
+
+        eq_(B.something,{
+                'foo':1,
+                'bazz':2,
+                })