PEP 205, Weak References -- initial checkin.

Lib/weakref.py

@@ -0,0 +1,117 @@
+"""Weak reference support for Python.
+
+This module is an implementation of PEP 205:
+
+http://python.sourceforge.net/peps/pep-0205.html
+"""
+
+import UserDict
+
+from _weakref import \
+     getweakrefcount, \
+     getweakrefs, \
+     ref, \
+     proxy, \
+     ReferenceError, \
+     CallableProxyType, \
+     ProxyType, \
+     ReferenceType
+
+ProxyTypes = (ProxyType, CallableProxyType)
+
+
+def mapping(dict=None):
+    return WeakDictionary(dict)
+
+
+class WeakDictionary(UserDict.UserDict):
+
+    # We inherit the constructor without worrying about the input
+    # dictionary; since it uses our .update() method, we get the right
+    # checks (if the other dictionary is a WeakDictionary, objects are
+    # unwrapped on the way out, and we always wrap on the way in).
+
+    def __getitem__(self, key):
+        o = self.data.get(key)()
+        if o is None:
+            raise KeyError, key
+        else:
+            return o
+
+    def __repr__(self):
+        return "<WeakDictionary at %s>" % id(self)
+
+    def __setitem__(self, key, value):
+        def remove(o, data=self.data, key=key):
+            del data[key]
+        self.data[key] = ref(value, remove)
+
+    def copy(self):
+        new = WeakDictionary()
+        for key, ref in self.data.items():
+            o = ref()
+            if o is not None:
+                new[key] = o
+
+    def get(self, key, default):
+        try:
+            ref = self.data[key]
+        except KeyError:
+            return default
+        else:
+            o = ref()
+            if o is None:
+                # This should only happen
+                return default
+            else:
+                return o
+
+    def items(self):
+        L = self.data.items()
+        for i in range(len(L)):
+            key, ref = L[i]
+            o = ref()
+            if o is not None:
+                L[i] = key, o
+        return L
+
+    def popitem(self):
+        while 1:
+            key, ref = self.data.popitem()
+            o = ref()
+            if o is not None:
+                return key, o
+
+    def setdefault(self, key, default):
+        try:
+            ref = self.data[key]
+        except KeyError:
+            def remove(o, data=self.data, key=key):
+                del data[key]
+            ref = ref(default, remove)
+            self.data[key] = ref
+            return default
+        else:
+            return ref()
+
+    def update(self, dict):
+        d = self.data
+        L = []
+        for key, o in dict.items():
+            def remove(o, data=d, key=key):
+                del data[key]
+            L.append(key, ref(o, remove))
+        for key, r in L:
+            d[key] = r
+
+    def values(self):
+        L = []
+        for ref in self.data.values():
+            o = ref()
+            if o is not None:
+                L.append(o)
+        return L
+
+
+# no longer needed
+del UserDict