"""Weak reference support for Python.

This module is an implementation of PEP 205:

https://peps.python.org/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,

_remove_dead_weakref)

from _weakrefset import WeakSet

import _collections_abc # Import after _weakref to avoid circular import.

import sys

import itertools

ProxyTypes = (ProxyType, CallableProxyType)

__all__ = ["ref", "proxy", "getweakrefcount", "getweakrefs",

"WeakKeyDictionary", "ReferenceType", "ProxyType",

"CallableProxyType", "ProxyTypes", "WeakValueDictionary",

"WeakSet", "WeakMethod", "finalize"]

_collections_abc.MutableSet.register(WeakSet)

class WeakMethod(ref):

"""

A custom `weakref.ref` subclass which simulates a weak reference to

a bound method, working around the lifetime problem of bound methods.

"""

__slots__ = "_func_ref", "_meth_type", "_alive", "__weakref__"

def __new__(cls, meth, callback=None):

try:

obj = meth.__self__

func = meth.__func__

except AttributeError:

raise TypeError("argument should be a bound method, not {}"

.format(type(meth))) from None

def _cb(arg):

# The self-weakref trick is needed to avoid creating a reference

# cycle.

self = self_wr()

if self._alive:

self._alive = False

if callback is not None:

callback(self)

self = ref.__new__(cls, obj, _cb)

self._func_ref = ref(func, _cb)

self._meth_type = type(meth)

self._alive = True

self_wr = ref(self)

return self

def __call__(self):

obj = super().__call__()

func = self._func_ref()

if obj is None or func is None:

return None

return self._meth_type(func, obj)

def __eq__(self, other):

if isinstance(other, WeakMethod):

if not self._alive or not other._alive:

return self is other

return ref.__eq__(self, other) and self._func_ref == other._func_ref

return NotImplemented

def __ne__(self, other):

if isinstance(other, WeakMethod):

if not self._alive or not other._alive:

return self is not other

return ref.__ne__(self, other) or self._func_ref != other._func_ref

return NotImplemented

__hash__ = ref.__hash__

class WeakValueDictionary(_collections_abc.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, other=(), /, **kw):

def remove(wr, selfref=ref(self), _atomic_removal=_remove_dead_weakref):

self = selfref()

if self is not None:

# Atomic removal is necessary since this function

# can be called asynchronously by the GC

_atomic_removal(self.data, wr.key)

self._remove = remove

self.data = {}

self.update(other, **kw)

def __getitem__(self, key):

o = self.data[key]()

if o is None:

raise KeyError(key)

else:

return o

def __delitem__(self, key):

del self.data[key]

def __len__(self):

return len(self.data)

def __contains__(self, key):

try:

o = self.data[key]()

except KeyError:

return False

return o is not None

def __repr__(self):

return "<%s at %#x>" % (self.__class__.__name__, id(self))

def __setitem__(self, key, value):

self.data[key] = KeyedRef(value, self._remove, key)

def copy(self):

new = WeakValueDictionary()

for key, wr in self.data.copy().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.copy().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):

for k, wr in self.data.copy().items():

v = wr()

if v is not None:

yield k, v

def keys(self):

for k, wr in self.data.copy().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.

"""

yield from self.data.copy().values()

def values(self):

for wr in self.data.copy().values():

obj = wr()

if obj is not None:

yield obj

def popitem(self):

while True:

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:

o = None

if o is None:

if args:

return args[0]

else:

raise KeyError(key)

else:

return o

def setdefault(self, key, default=None):

try:

o = self.data[key]()

except KeyError:

o = None

if o is None:

self.data[key] = KeyedRef(default, self._remove, key)

return default

else:

return o

def update(self, other=None, /, **kwargs):

d = self.data

if other is not None:

if not hasattr(other, "items"):

other = dict(other)

for key, o in other.items():

d[key] = KeyedRef(o, self._remove, key)

for key, o in kwargs.items():

d[key] = KeyedRef(o, self._remove, key)

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.copy().values())

def __ior__(self, other):

self.update(other)

return self

def __or__(self, other):

if isinstance(other, _collections_abc.Mapping):

c = self.copy()

c.update(other)

return c

return NotImplemented

def __ror__(self, other):

if isinstance(other, _collections_abc.Mapping):

c = self.__class__()

c.update(other)

c.update(self)

return c

return NotImplemented

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_abc.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:

try:

del self.data[k]

except KeyError:

pass

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 __len__(self):

return len(self.data)

def __repr__(self):

return "<%s at %#x>" % (self.__class__.__name__, 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.copy().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.copy().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):

for wr, value in self.data.copy().items():

key = wr()

if key is not None:

yield key, value

def keys(self):

for wr in self.data.copy():

obj = wr()

if obj is not None:

yield obj

__iter__ = keys

def values(self):

for wr, value in self.data.copy().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):

if kwargs:

msg = ("Keyword arguments are not supported: "

"cannot create weak reference to 'str' object")

raise TypeError(msg)

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

def __ior__(self, other):

self.update(other)

return self

def __or__(self, other):

if isinstance(other, _collections_abc.Mapping):

c = self.copy()

c.update(other)

return c

return NotImplemented

def __ror__(self, other):

if isinstance(other, _collections_abc.Mapping):

c = self.__class__()

c.update(other)

c.update(self)

return c

return NotImplemented

class finalize:

"""Class for finalization of weakrefable objects

finalize(obj, func, *args, **kwargs) returns a callable finalizer

object which will be called when obj is garbage collected. The

first time the finalizer is called it evaluates func(*arg, **kwargs)

and returns the result. After this the finalizer is dead, and

calling it just returns None.

When the program exits any remaining finalizers for which the

atexit attribute is true will be run in reverse order of creation.

By default atexit is true.

"""

# Finalizer objects don't have any state of their own. They are

# just used as keys to lookup _Info objects in the registry. This

# ensures that they cannot be part of a ref-cycle.

__slots__ = ()

_registry = {}

_shutdown = False

_index_iter = itertools.count()

_dirty = False

_registered_with_atexit = False

class _Info:

__slots__ = ("weakref", "func", "args", "kwargs", "atexit", "index")

def __init__(self, obj, func, /, *args, **kwargs):

if not self._registered_with_atexit:

# We may register the exit function more than once because

# of a thread race, but that is harmless

import atexit

atexit.register(self._exitfunc)

finalize._registered_with_atexit = True

info = self._Info()

info.weakref = ref(obj, self)

info.func = func

info.args = args

info.kwargs = kwargs or None

info.atexit = True

info.index = next(self._index_iter)

self._registry[self] = info

finalize._dirty = True

def __call__(self, _=None):

"""If alive then mark as dead and return func(*args, **kwargs);

otherwise return None"""

info = self._registry.pop(self, None)

if info and not self._shutdown:

return info.func(*info.args, **(info.kwargs or {}))

def detach(self):

"""If alive then mark as dead and return (obj, func, args, kwargs);

otherwise return None"""

info = self._registry.get(self)

obj = info and info.weakref()

if obj is not None and self._registry.pop(self, None):

return (obj, info.func, info.args, info.kwargs or {})

def peek(self):

"""If alive then return (obj, func, args, kwargs);

otherwise return None"""

info = self._registry.get(self)

obj = info and info.weakref()

if obj is not None:

return (obj, info.func, info.args, info.kwargs or {})

@property

def alive(self):

"""Whether finalizer is alive"""

return self in self._registry

@property

def atexit(self):

"""Whether finalizer should be called at exit"""

info = self._registry.get(self)

return bool(info) and info.atexit

@atexit.setter

def atexit(self, value):

info = self._registry.get(self)

if info:

info.atexit = bool(value)

def __repr__(self):

info = self._registry.get(self)

obj = info and info.weakref()

if obj is None:

return '<%s object at %#x; dead>' % (type(self).__name__, id(self))

else:

return '<%s object at %#x; for %r at %#x>' % \

(type(self).__name__, id(self), type(obj).__name__, id(obj))

@classmethod

def _select_for_exit(cls):

# Return live finalizers marked for exit, oldest first

L = [(f,i) for (f,i) in cls._registry.items() if i.atexit]

L.sort(key=lambda item:item[1].index)

return [f for (f,i) in L]

@classmethod

def _exitfunc(cls):

# At shutdown invoke finalizers for which atexit is true.

# This is called once all other non-daemonic threads have been

# joined.

reenable_gc = False

try:

if cls._registry:

import gc

if gc.isenabled():

reenable_gc = True

gc.disable()

pending = None

while True:

if pending is None or finalize._dirty:

pending = cls._select_for_exit()

finalize._dirty = False

if not pending:

break

f = pending.pop()

try:

# gc is disabled, so (assuming no daemonic

# threads) the following is the only line in

# this function which might trigger creation

# of a new finalizer

f()

except Exception:

sys.excepthook(*sys.exc_info())

assert f not in cls._registry

finally:

# prevent any more finalizers from executing during shutdown

finalize._shutdown = True

if reenable_gc:

gc.enable()