diff options
Diffstat (limited to 'lib/sqlalchemy/util/_collections.py')
| -rw-r--r-- | lib/sqlalchemy/util/_collections.py | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/lib/sqlalchemy/util/_collections.py b/lib/sqlalchemy/util/_collections.py index 04409cfd9..7b46bc8e6 100644 --- a/lib/sqlalchemy/util/_collections.py +++ b/lib/sqlalchemy/util/_collections.py @@ -676,10 +676,13 @@ class IdentitySet(object): class WeakSequence(object): def __init__(self, __elements=()): + # adapted from weakref.WeakKeyDictionary, prevent reference + # cycles in the collection itself def _remove(item, selfref=weakref.ref(self)): self = selfref() if self is not None: self._storage.remove(item) + self._remove = _remove self._storage = [ weakref.ref(element, _remove) for element in __elements @@ -737,6 +740,22 @@ class PopulateDict(dict): return val +class WeakPopulateDict(dict): + """Like PopulateDict, but assumes a self + a method and does not create + a reference cycle. + + """ + + def __init__(self, creator_method): + self.creator = creator_method.__func__ + weakself = creator_method.__self__ + self.weakself = weakref.ref(weakself) + + def __missing__(self, key): + self[key] = val = self.creator(self.weakself(), key) + return val + + # Define collections that are capable of storing # ColumnElement objects as hashable keys/elements. # At this point, these are mostly historical, things @@ -744,7 +763,6 @@ class PopulateDict(dict): column_set = set column_dict = dict ordered_column_set = OrderedSet -populate_column_dict = PopulateDict _getters = PopulateDict(operator.itemgetter) |