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|
"""Weak reference support for Python.
This module is an implementation of PEP 205:
http://python.sourceforge.net/peps/pep-0205.html
"""
# Naming convention: Variables named "wr" are weak reference objects;
# they are called this instead of "ref" to avoid name collisions with
# the module-global ref() function imported from _weakref.
import UserDict
from _weakref import \
getweakrefcount, \
getweakrefs, \
ref, \
proxy, \
ReferenceError, \
CallableProxyType, \
ProxyType, \
ReferenceType
ProxyTypes = (ProxyType, CallableProxyType)
__all__ = ["ref", "proxy", "getweakrefcount", "getweakrefs",
"WeakKeyDictionary", "ReferenceType", "ProxyType",
"CallableProxyType", "ProxyTypes", "WeakValueDictionary"]
class WeakValueDictionary(UserDict.UserDict):
"""Mapping class that references values weakly.
Entries in the dictionary will be discarded when no strong
reference to the value exists anymore
"""
# 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 WeakValueDictionary,
# 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 "<WeakValueDictionary 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 = WeakValueDictionary()
for key, wr in self.data.items():
o = wr()
if o is not None:
new[key] = o
return new
def get(self, key, default=None):
try:
wr = self.data[key]
except KeyError:
return default
else:
o = wr()
if o is None:
# This should only happen
return default
else:
return o
def items(self):
L = []
for key, wr in self.data.items():
o = wr()
if o is not None:
L.append((key, o))
return L
def popitem(self):
while 1:
key, wr = self.data.popitem()
o = wr()
if o is not None:
return key, o
def setdefault(self, key, default):
try:
wr = self.data[key]
except KeyError:
def remove(o, data=self.data, key=key):
del data[key]
self.data[key] = ref(default, remove)
return default
else:
return wr()
def update(self, dict):
d = self.data
for key, o in dict.items():
def remove(o, data=d, key=key):
del data[key]
d[key] = ref(o, remove)
def values(self):
L = []
for wr in self.data.values():
o = wr()
if o is not None:
L.append(o)
return L
class WeakKeyDictionary(UserDict.UserDict):
""" Mapping class that references keys weakly.
Entries in the dictionary will be discarded when there is no
longer a strong reference to the key. This can be used to
associate additional data with an object owned by other parts of
an application without adding attributes to those objects. This
can be especially useful with objects that override attribute
accesses.
"""
def __init__(self, dict=None):
self.data = {}
if dict is not None: self.update(dict)
def remove(k, data=self.data):
del data[k]
self._remove = remove
def __getitem__(self, key):
return self.data[ref(key)]
def __repr__(self):
return "<WeakKeyDictionary at %s>" % id(self)
def __setitem__(self, key, value):
self.data[ref(key, self._remove)] = value
def copy(self):
new = WeakKeyDictionary()
for key, value in self.data.items():
o = key()
if o is not None:
new[o] = value
return new
def get(self, key, default=None):
return self.data.get(ref(key),default)
def has_key(self, key):
return self.data.has_key(ref(key))
def items(self):
L = []
for key, value in self.data.items():
o = key()
if o is not None:
L.append((o, value))
return L
def keys(self):
L = []
for wr in self.data.keys():
o = wr()
if o is not None:
L.append(o)
return L
def popitem(self):
while 1:
key, value = self.data.popitem()
o = key()
if o is not None:
return o, value
def setdefault(self, key, default):
return self.data.setdefault(ref(key, self._remove),default)
def update(self, dict):
d = self.data
for key, value in dict.items():
d[ref(key, self._remove)] = value
# no longer needed
del UserDict
|
