Lib/weakref.py

   1 """Weak reference support for Python.
   2
   3 This module is an implementation of PEP 205:
   4
   5 http://python.sourceforge.net/peps/pep-0205.html
   6 """
   7
   8 # Naming convention: Variables named "wr" are weak reference objects;
   9 # they are called this instead of "ref" to avoid name collisions with
  10 # the module-global ref() function imported from _weakref.
  11
  12 import UserDict
  13
  14 from _weakref import \
  15      getweakrefcount, \
  16      getweakrefs, \
  17      ref, \
  18      proxy, \
  19      ReferenceError, \
  20      CallableProxyType, \
  21      ProxyType, \
  22      ReferenceType
  23
  24 ProxyTypes = (ProxyType, CallableProxyType)
  25
  26 __all__ = ["ref", "proxy", "getweakrefcount", "getweakrefs",
  27            "WeakKeyDictionary", "ReferenceType", "ProxyType",
  28            "CallableProxyType", "ProxyTypes", "WeakValueDictionary"]
  29
  30
  31 class WeakValueDictionary(UserDict.UserDict):
  32     """Mapping class that references values weakly.
  33
  34     Entries in the dictionary will be discarded when no strong
  35     reference to the value exists anymore
  36     """
  37     # We inherit the constructor without worrying about the input
  38     # dictionary; since it uses our .update() method, we get the right
  39     # checks (if the other dictionary is a WeakValueDictionary,
  40     # objects are unwrapped on the way out, and we always wrap on the
  41     # way in).
  42
  43     def __getitem__(self, key):
  44         o = self.data.get(key)()
  45         if o is None:
  46             raise KeyError, key
  47         else:
  48             return o
  49
  50     def __repr__(self):
  51         return "<WeakValueDictionary at %s>" % id(self)
  52
  53     def __setitem__(self, key, value):
  54         def remove(o, data=self.data, key=key):
  55             del data[key]
  56         self.data[key] = ref(value, remove)
  57
  58     def copy(self):
  59         new = WeakValueDictionary()
  60         for key, wr in self.data.items():
  61             o = wr()
  62             if o is not None:
  63                 new[key] = o
  64         return new
  65
  66     def get(self, key, default=None):
  67         try:
  68             wr = self.data[key]
  69         except KeyError:
  70             return default
  71         else:
  72             o = wr()
  73             if o is None:
  74                 # This should only happen
  75                 return default
  76             else:
  77                 return o
  78
  79     def items(self):
  80         L = []
  81         for key, wr in self.data.items():
  82             o = wr()
  83             if o is not None:
  84                 L.append((key, o))
  85         return L
  86
  87     def popitem(self):
  88         while 1:
  89             key, wr = self.data.popitem()
  90             o = wr()
  91             if o is not None:
  92                 return key, o
  93
  94     def setdefault(self, key, default):
  95         try:
  96             wr = self.data[key]
  97         except KeyError:
  98             def remove(o, data=self.data, key=key):
  99                 del data[key]
 100             self.data[key] = ref(default, remove)
 101             return default
 102         else:
 103             return wr()
 104
 105     def update(self, dict):
 106         d = self.data
 107         for key, o in dict.items():
 108             def remove(o, data=d, key=key):
 109                 del data[key]
 110             d[key] = ref(o, remove)
 111
 112     def values(self):
 113         L = []
 114         for wr in self.data.values():
 115             o = wr()
 116             if o is not None:
 117                 L.append(o)
 118         return L
 119
 120
 121 class WeakKeyDictionary(UserDict.UserDict):
 122     """ Mapping class that references keys weakly.
 123
 124     Entries in the dictionary will be discarded when there is no
 125     longer a strong reference to the key. This can be used to
 126     associate additional data with an object owned by other parts of
 127     an application without adding attributes to those objects. This
 128     can be especially useful with objects that override attribute
 129     accesses.
 130     """
 131
 132     def __init__(self, dict=None):
 133         self.data = {}
 134         if dict is not None: self.update(dict)
 135         def remove(k, data=self.data):
 136             del data[k]
 137         self._remove = remove
 138
 139     def __getitem__(self, key):
 140         return self.data[ref(key)]
 141
 142     def __repr__(self):
 143         return "<WeakKeyDictionary at %s>" % id(self)
 144
 145     def __setitem__(self, key, value):
 146         self.data[ref(key, self._remove)] = value
 147
 148     def copy(self):
 149         new = WeakKeyDictionary()
 150         for key, value in self.data.items():
 151             o = key()
 152             if o is not None:
 153                 new[o] = value
 154         return new
 155
 156     def get(self, key, default=None):
 157         return self.data.get(ref(key),default)
 158
 159     def has_key(self, key):
 160         return self.data.has_key(ref(key))
 161
 162     def items(self):
 163         L = []
 164         for key, value in self.data.items():
 165             o = key()
 166             if o is not None:
 167                 L.append((o, value))
 168         return L
 169
 170     def keys(self):
 171         L = []
 172         for wr in self.data.keys():
 173             o = wr()
 174             if o is not None:
 175                 L.append(o)
 176         return L
 177
 178     def popitem(self):
 179         while 1:
 180             key, value = self.data.popitem()
 181             o = key()
 182             if o is not None:
 183                 return o, value
 184
 185     def setdefault(self, key, default):
 186         return self.data.setdefault(ref(key, self._remove),default)
 187
 188     def update(self, dict):
 189         d = self.data
 190         for key, value in dict.items():
 191             d[ref(key, self._remove)] = value
 192
 193
 194 # no longer needed
 195 del UserDict