"""Weak reference support for Python.
This module is an implementation of PEP 205:
http://www.python.org/dev/peps/pep-0205/
"""
# 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.
from _weakref import (
getweakrefcount,
getweakrefs,
ref,
proxy,
CallableProxyType,
ProxyType,
ReferenceType)
from _weakrefset import WeakSet, _IterationGuard
import collections # Import after _weakref to avoid circular import.
ProxyTypes = (ProxyType, CallableProxyType)
__all__ = ["ref", "proxy", "getweakrefcount", "getweakrefs",
"WeakKeyDictionary", "ReferenceType", "ProxyType",
"CallableProxyType", "ProxyTypes", "WeakValueDictionary",
"WeakSet"]
class WeakValueDictionary(collections.MutableMapping):
"""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 __init__(self, *args, **kw):
def remove(wr, selfref=ref(self)):
self = selfref()
if self is not None:
if self._iterating:
self._pending_removals.append(wr.key)
else:
del self.data[wr.key]
self._remove = remove
# A list of keys to be removed
self._pending_removals = []
self._iterating = set()
self.data = d = {}
self.update(*args, **kw)
def _commit_removals(self):
l = self._pending_removals
d = self.data
# We shouldn't encounter any KeyError, because this method should
# always be called *before* mutating the dict.
while l:
del d[l.pop()]
def __getitem__(self, key):
o = self.data[key]()
if o is None:
raise KeyError(key)
else:
return o
def __delitem__(self, key):
if self._pending_removals:
self._commit_removals()
del self.data[key]
def __len__(self):
return len(self.data) - len(self._pending_removals)
def __contains__(self, key):
try:
o = self.data[key]()
except KeyError:
return False
return o is not None
def __repr__(self):
return "<WeakValueDictionary at %s>" % id(self)
def __setitem__(self, key, value):
if self._pending_removals:
self._commit_removals()
self.data[key] = KeyedRef(value, self._remove, 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
__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]
except KeyError:
return default
else:
o = wr()
if o is None:
# This should only happen
return default
else:
return o
def items(self):
with _IterationGuard(self):
for k, wr in self.data.items():
v = wr()
if v is not None:
yield k, v
def keys(self):
with _IterationGuard(self):
for k, wr in self.data.items():
if wr() is not None:
yield k
__iter__ = keys
def itervaluerefs(self):
"""Return an iterator that yields the weak references to the values.
The references are not guaranteed to be 'live' at the time
they are used, so the result of calling the references needs
to be checked before being used. This can be used to avoid
creating references that will cause the garbage collector to
keep the values around longer than needed.
"""
with _IterationGuard(self):
for wr in self.data.values():
yield wr
def values(self):
with _IterationGuard(self):
for wr in self.data.values():
obj = wr()
if obj is not None:
yield obj
def popitem(self):
if self._pending_removals:
self._commit_removals()
while True:
key, wr = self.data.popitem()
o = wr()
if o is not None:
return key, o
def pop(self, key, *args):
if self._pending_removals:
self._commit_removals()
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=None):
try:
wr = self.data[key]
except KeyError:
if self._pending_removals:
self._commit_removals()
self.data[key] = KeyedRef(default, self._remove, key)
return default
else:
return wr()
def update(self, dict=None, **kwargs):
if self._pending_removals:
self._commit_removals()
d = self.data
if dict is not None:
if not hasattr(dict, "items"):
dict = type({})(dict)
for key, o in dict.items():
d[key] = KeyedRef(o, self._remove, key)
if len(kwargs):
self.update(kwargs)
def valuerefs(self):
"""Return a list of weak references to the values.
The references are not guaranteed to be 'live' at the time
they are used, so the result of calling the references needs
to be checked before being used. This can be used to avoid
creating references that will cause the garbage collector to
keep the values around longer than needed.
"""
return list(self.data.values())
class KeyedRef(ref):
"""Specialized reference that includes a key corresponding to the value.
This is used in the WeakValueDictionary to avoid having to create
a function object for each key stored in the mapping. A shared
callback object can use the 'key' attribute of a KeyedRef instead
of getting a reference to the key from an enclosing scope.
"""
__slots__ = "key",
def __new__(type, ob, callback, key):
self = ref.__new__(type, ob, callback)
self.key = key
return self
def __init__(self, ob, callback, key):
super().__init__(ob, callback)
class WeakKeyDictionary(collections.MutableMapping):
""" 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:
if self._iterating:
self._pending_removals.append(k)
else:
del self.data[k]
self._remove = remove
# A list of dead weakrefs (keys to be removed)
self._pending_removals = []
self._iterating = set()
if dict is not None:
self.update(dict)
def _commit_removals(self):
# NOTE: We don't need to call this method before mutating the dict,
# because a dead weakref never compares equal to a live weakref,
# even if they happened to refer to equal objects.
# However, it means keys may already have been removed.
l = self._pending_removals
d = self.data
while l:
try:
del d[l.pop()]
except KeyError:
pass
def __delitem__(self, key):
del self.data[ref(key)]
def __getitem__(self, key):
return self.data[ref(key)]
def __len__(self):
return len(self.data) - len(self._pending_removals)
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
__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)
def __contains__(self, key):
try:
wr = ref(key)
except TypeError:
return False
return wr in self.data
def items(self):
with _IterationGuard(self):
for wr, value in self.data.items():
key = wr()
if key is not None:
yield key, value
def keys(self):
with _IterationGuard(self):
for wr in self.data:
obj = wr()
if obj is not None:
yield obj
__iter__ = keys
def values(self):
with _IterationGuard(self):
for wr, value in self.data.items():
if wr() is not None:
yield value
def keyrefs(self):
"""Return a list of weak references to the keys.
The references are not guaranteed to be 'live' at the time
they are used, so the result of calling the references needs
to be checked before being used. This can be used to avoid
creating references that will cause the garbage collector to
keep the keys around longer than needed.
"""
return list(self.data)
def popitem(self):
while True:
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=None):
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)
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