Issue #2116: Weak references and weak dictionaries now support copy()ing and deepcopy()ing.

Lib/copy.py

@@ -49,6 +49,7 @@ __getstate__() and __setstate__().  See the documentation for module
 """
 
 import types
+import weakref
 from copy_reg import dispatch_table
 
 class Error(Exception):
@@ -102,7 +103,7 @@ def _copy_immutable(x):
 for t in (type(None), int, long, float, bool, str, tuple,
           frozenset, type, xrange, types.ClassType,
           types.BuiltinFunctionType, type(Ellipsis),
-          types.FunctionType):
+          types.FunctionType, weakref.ref):
     d[t] = _copy_immutable
 for name in ("ComplexType", "UnicodeType", "CodeType"):
     t = getattr(types, name, None)
@@ -220,6 +221,7 @@ d[xrange] = _deepcopy_atomic
 d[types.ClassType] = _deepcopy_atomic
 d[types.BuiltinFunctionType] = _deepcopy_atomic
 d[types.FunctionType] = _deepcopy_atomic
+d[weakref.ref] = _deepcopy_atomic
 
 def _deepcopy_list(x, memo):
     y = []

Lib/test/test_copy.py

@@ -2,6 +2,8 @@
 
 import copy
 import copy_reg
+import weakref
+import operator
 
 import unittest
 from test import test_support
@@ -585,6 +587,92 @@ class TestCopy(unittest.TestCase):
         bar = lambda: None
         self.assertEqual(copy.deepcopy(bar), bar)
 
+    def _check_weakref(self, _copy):
+        class C(object):
+            pass
+        obj = C()
+        x = weakref.ref(obj)
+        y = _copy(x)
+        self.assertTrue(y is x)
+        del obj
+        y = _copy(x)
+        self.assertTrue(y is x)
+
+    def test_copy_weakref(self):
+        self._check_weakref(copy.copy)
+
+    def test_deepcopy_weakref(self):
+        self._check_weakref(copy.deepcopy)
+
+    def _check_copy_weakdict(self, _dicttype):
+        class C(object):
+            pass
+        a, b, c, d = [C() for i in xrange(4)]
+        u = _dicttype()
+        u[a] = b
+        u[c] = d
+        v = copy.copy(u)
+        self.assertFalse(v is u)
+        self.assertEqual(v, u)
+        self.assertEqual(v[a], b)
+        self.assertEqual(v[c], d)
+        self.assertEqual(len(v), 2)
+        del c, d
+        self.assertEqual(len(v), 1)
+        x, y = C(), C()
+        # The underlying containers are decoupled
+        v[x] = y
+        self.assertFalse(x in u)
+
+    def test_copy_weakkeydict(self):
+        self._check_copy_weakdict(weakref.WeakKeyDictionary)
+
+    def test_copy_weakvaluedict(self):
+        self._check_copy_weakdict(weakref.WeakValueDictionary)
+
+    def test_deepcopy_weakkeydict(self):
+        class C(object):
+            def __init__(self, i):
+                self.i = i
+        a, b, c, d = [C(i) for i in xrange(4)]
+        u = weakref.WeakKeyDictionary()
+        u[a] = b
+        u[c] = d
+        # Keys aren't copied, values are
+        v = copy.deepcopy(u)
+        self.assertNotEqual(v, u)
+        self.assertEqual(len(v), 2)
+        self.assertFalse(v[a] is b)
+        self.assertFalse(v[c] is d)
+        self.assertEqual(v[a].i, b.i)
+        self.assertEqual(v[c].i, d.i)
+        del c
+        self.assertEqual(len(v), 1)
+
+    def test_deepcopy_weakvaluedict(self):
+        class C(object):
+            def __init__(self, i):
+                self.i = i
+        a, b, c, d = [C(i) for i in xrange(4)]
+        u = weakref.WeakValueDictionary()
+        u[a] = b
+        u[c] = d
+        # Keys are copied, values aren't
+        v = copy.deepcopy(u)
+        self.assertNotEqual(v, u)
+        self.assertEqual(len(v), 2)
+        (x, y), (z, t) = sorted(v.items(), key=lambda (k, v): k.i)
+        self.assertFalse(x is a)
+        self.assertEqual(x.i, a.i)
+        self.assertTrue(y is b)
+        self.assertFalse(z is c)
+        self.assertEqual(z.i, c.i)
+        self.assertTrue(t is d)
+        del x, y, z, t
+        del d
+        self.assertEqual(len(v), 1)
+
+
 def global_foo(x, y): return x+y
 
 def test_main():

Lib/weakref.py

@@ -85,6 +85,17 @@ class WeakValueDictionary(UserDict.UserDict):
                 new[key] = o
         return new
 
+    __copy__ = copy
+
+    def __deepcopy__(self, memo):
+        from copy import deepcopy
+        new = self.__class__()
+        for key, wr in self.data.items():
+            o = wr()
+            if o is not None:
+                new[deepcopy(key, memo)] = o
+        return new
+
     def get(self, key, default=None):
         try:
             wr = self.data[key]
@@ -256,6 +267,17 @@ class WeakKeyDictionary(UserDict.UserDict):
                 new[o] = value
         return new
 
+    __copy__ = copy
+
+    def __deepcopy__(self, memo):
+        from copy import deepcopy
+        new = self.__class__()
+        for key, value in self.data.items():
+            o = key()
+            if o is not None:
+                new[o] = deepcopy(value, memo)
+        return new
+
     def get(self, key, default=None):
         return self.data.get(ref(key),default)
 

Misc/NEWS

@@ -293,6 +293,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #2116: Weak references and weak dictionaries now support copy()ing and
+  deepcopy()ing.
+
 - Issue #1655: Make imaplib IPv6-capable. Patch by Derek Morr.
 
 - Issue #5918: Fix a crash in the parser module.