- [feature] *Very limited* support for

    inheriting mappers to be GC'ed when the
    class itself is deferenced.  The mapper
    must not have its own table (i.e.
    single table inh only) without polymorphic
    attributes in place.
    This allows for the use case of
    creating a temporary subclass of a declarative
    mapped class, with no table or mapping
    directives of its own, to be garbage collected
    when dereferenced by a unit test.
    [ticket:2526]

1 files changed, 21 insertions, 0 deletions

diff --git a/lib/sqlalchemy/util/compat.py b/lib/sqlalchemy/util/compat.py
index 5dc59b5c5..215a68e91 100644
--- a/lib/sqlalchemy/util/compat.py
+++ b/lib/sqlalchemy/util/compat.py
@@ -166,6 +166,27 @@ except ImportError:
             return 'defaultdict(%s, %s)' % (self.default_factory,
                                             dict.__repr__(self))
 
+try:
+    from weakref import WeakSet
+except:
+    import weakref
+
+    class WeakSet(object):
+        """Implement the small subset of set() which SQLAlchemy needs
+        here. """
+        def __init__(self, values=None):
+            self._storage = weakref.WeakKeyDictionary()
+            if values is not None:
+                self._storage.update((value, None) for value in values)
+
+        def __iter__(self):
+            return iter(self._storage)
+
+        def union(self, other):
+            return WeakSet(set(self).union(other))
+
+        def add(self, other):
+            self._storage[other] = True
 
 # find or create a dict implementation that supports __missing__
 class _probe(dict):