python中的weakref列表 [英] weakref list in python

问题描述

我需要一个弱引用列表，用于在项目死亡时删除项目.目前我这样做的唯一方法是不断刷新列表(手动删除无效引用).

I'm in need of a list of weak references that deletes items when they die. Currently the only way I have of doing this is to keep flushing the list (removing dead references manually).

我知道有一个 WeakKeyDictionary 和一个 WeakValueDictionary，但我真的想要一个 WeakList，有没有办法做到这一点?

I'm aware there's a WeakKeyDictionary and a WeakValueDictionary, but I'm really after a WeakList, is there a way of doing this?

这是一个例子:

import weakref

class A(object):
    def __init__(self):
       pass

class B(object):
    def __init__(self):
        self._references = []

    def addReference(self, obj):
        self._references.append(weakref.ref(obj))

    def flush(self):
        toRemove = []

        for ref in self._references:
            if ref() is None:
                toRemove.append(ref)

        for item in toRemove:
            self._references.remove(item)

b = B()

a1 = A()
b.addReference(a1)
a2 = A()
b.addReference(a2)

del a1
b.flush()
del a2
b.flush()

推荐答案

您可以自己实现它，与您的做法类似，但使用一个在尝试访问项目之前调用 flush() 的列表子类.

You could implement it yourself, similarly to how you have done, but with a list subclass that calls flush() before attempting to access an item.

显然，您不想在每次访问时都这样做，但是您可以通过在弱引用上设置回调以在某些内容死亡时将列表标记为脏来优化此操作.然后您只需要在自上次访问后某些内容死亡时刷新列表.

Obviously you don't want to do this on every access, but you can optimize this by setting a callback on the weak reference to mark the list dirty when something dies. Then you only need to flush the list when something has died since the last access.

这是使用此方法实现的列表类.(请注意，它没有经过太多测试，并且某些方法的实现效率不高(例如，那些只是转换为真实列表并在其上调用方法的方法)，但它应该是一个合理的起点:

Here's a list class implemented using this method. (Note that it's not tested much, and some methods aren't implemented very efficiently (eg. those which just convert to a real list and call the method on that), but it should be a reasonable starting point:

import weakref

class WeakList(list):
    def __init__(self, seq=()):
        list.__init__(self)
        self._refs = []
        self._dirty=False
        for x in seq: self.append(x)

    def _mark_dirty(self, wref):
        self._dirty = True

    def flush(self):
        self._refs = [x for x in self._refs if x() is not None]
        self._dirty=False

    def __getitem__(self, idx):
        if self._dirty: self.flush()
        return self._refs[idx]()

    def __iter__(self):
        for ref in self._refs:
            obj = ref()
            if obj is not None: yield obj

    def __repr__(self):
        return "WeakList(%r)" % list(self)

    def __len__(self):
        if self._dirty: self.flush()
        return len(self._refs)

    def __setitem__(self, idx, obj):
        if isinstance(idx, slice):
            self._refs[idx] = [weakref.ref(obj, self._mark_dirty) for x in obj]
        else:
            self._refs[idx] = weakref.ref(obj, self._mark_dirty)

    def __delitem__(self, idx):
        del self._refs[idx]

    def append(self, obj):
        self._refs.append(weakref.ref(obj, self._mark_dirty))

    def count(self, obj):
        return list(self).count(obj)

    def extend(self, items):
        for x in items: self.append(x)

    def index(self, obj):
        return list(self).index(obj)

    def insert(self, idx, obj):
        self._refs.insert(idx, weakref.ref(obj, self._mark_dirty))

    def pop(self, idx):
        if self._dirty: self.flush()
        obj=self._refs[idx]()
        del self._refs[idx]
        return obj

    def remove(self, obj):
        if self._dirty: self.flush() # Ensure all valid.
        for i, x in enumerate(self):
            if x == obj:
                del self[i]

    def reverse(self):
        self._refs.reverse()

    def sort(self, cmp=None, key=None, reverse=False):
        if self._dirty: self.flush()
        if key is not None:
            key = lambda x,key=key: key(x())
        else:
            key = apply
        self._refs.sort(cmp=cmp, key=key, reverse=reverse)

    def __add__(self, other):
        l = WeakList(self)
        l.extend(other)
        return l

    def __iadd__(self, other):
        self.extend(other)
        return self

    def __contains__(self, obj):
        return obj in list(self)

    def __mul__(self, n):
        return WeakList(list(self)*n)

    def __imul__(self, n):
        self._refs *= n
        return self

添加更完整的列表实现.

Add a more complete list implementation.

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