cpython/Lib/weakref.py

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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, \
CallableProxyType, \
ProxyType, \
ReferenceType
from exceptions import ReferenceError
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[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):
self.data[key] = ref(value, self.__makeremove(key))
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 iteritems(self):
return WeakValuedItemIterator(self)
def iterkeys(self):
return self.data.iterkeys()
__iter__ = iterkeys
def itervalues(self):
return WeakValuedValueIterator(self)
def popitem(self):
while 1:
key, wr = self.data.popitem()
o = wr()
if o is not None:
return key, o
def pop(self, key, *args):
try:
o = self.data.pop(key)()
except KeyError:
if args:
return args[0]
raise
if o is None:
raise KeyError, key
else:
return o
def setdefault(self, key, default):
try:
wr = self.data[key]
except KeyError:
self.data[key] = ref(default, self.__makeremove(key))
return default
else:
return wr()
def update(self, dict=None, **kwargs):
d = self.data
if dict is not None:
if not hasattr(dict, "items"):
dict = type({})(dict)
for key, o in dict.items():
d[key] = ref(o, self.__makeremove(key))
if len(kwargs):
self.update(kwargs)
def values(self):
L = []
for wr in self.data.values():
o = wr()
if o is not None:
L.append(o)
return L
def __makeremove(self, key):
def remove(o, selfref=ref(self), key=key):
self = selfref()
if self is not None:
del self.data[key]
return remove
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 = {}
def remove(k, selfref=ref(self)):
self = selfref()
if self is not None:
del self.data[k]
self._remove = remove
if dict is not None: self.update(dict)
def __delitem__(self, key):
del self.data[ref(key)]
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):
try:
wr = ref(key)
except TypeError:
return 0
return wr in self.data
def __contains__(self, key):
try:
wr = ref(key)
except TypeError:
return 0
return wr in self.data
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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 iteritems(self):
return WeakKeyedItemIterator(self)
def iterkeys(self):
return WeakKeyedKeyIterator(self)
__iter__ = iterkeys
def itervalues(self):
return self.data.itervalues()
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 pop(self, key, *args):
return self.data.pop(ref(key), *args)
def setdefault(self, key, default):
return self.data.setdefault(ref(key, self._remove),default)
def update(self, dict=None, **kwargs):
d = self.data
if dict is not None:
if not hasattr(dict, "items"):
dict = type({})(dict)
for key, value in dict.items():
d[ref(key, self._remove)] = value
if len(kwargs):
self.update(kwargs)
class BaseIter:
def __iter__(self):
return self
class WeakKeyedKeyIterator(BaseIter):
def __init__(self, weakdict):
self._next = weakdict.data.iterkeys().next
def next(self):
while 1:
wr = self._next()
obj = wr()
if obj is not None:
return obj
class WeakKeyedItemIterator(BaseIter):
def __init__(self, weakdict):
self._next = weakdict.data.iteritems().next
def next(self):
while 1:
wr, value = self._next()
key = wr()
if key is not None:
return key, value
class WeakValuedValueIterator(BaseIter):
def __init__(self, weakdict):
self._next = weakdict.data.itervalues().next
def next(self):
while 1:
wr = self._next()
obj = wr()
if obj is not None:
return obj
class WeakValuedItemIterator(BaseIter):
def __init__(self, weakdict):
self._next = weakdict.data.iteritems().next
def next(self):
while 1:
key, wr = self._next()
value = wr()
if value is not None:
return key, value
# no longer needed
del UserDict