Python中可索引的弱有序集 [英] Indexable weak ordered set in Python

问题描述

我想知道是否有一种简单的方法可以在Python中构建一个可索引的弱有序集。我试着自己建一个。这就是我想出的：

I was wondering if there is an easy way to build an indexable weak ordered set in Python. I tried to build one myself. Here's what I came up with:

"""
An indexable, ordered set of objects, which are held by weak reference.
"""
from nose.tools import *
import blist
import weakref


class WeakOrderedSet(blist.weaksortedset):
    """
    A blist.weaksortedset whose key is the insertion order.
    """
    def __init__(self, iterable=()):
        self.insertion_order = weakref.WeakKeyDictionary()  # value_type to int
        self.last_key = 0
        super().__init__(key=self.insertion_order.__getitem__)
        for item in iterable:
            self.add(item)

    def __delitem__(self, index):
        values = super().__getitem__(index)
        super().__delitem__(index)
        if not isinstance(index, slice):
            # values is just one element
            values = [values]
        for value in values:
            if value not in self:
                del self.insertion_order[value]

    def add(self, value):
        # Choose a key so that value is on the end.
        if value not in self.insertion_order:
            key = self.last_key
            self.last_key += 1
            self.insertion_order[value] = key
        super().add(value)

    def discard(self, value):
        super().discard(value)
        if value not in self:
            del self.insertion_order[value]

    def remove(self, value):
        super().remove(value)
        if value not in self:
            del self.insertion_order[value]

    def pop(self, *args, **kwargs):
        value = super().pop(*args, **kwargs)
        if value not in self:
            del self.insertion_order[value]

    def clear(self):
        super().clear()
        self.insertion_order.clear()

    def update(self, *args):
        for arg in args:
            for item in arg:
                self.add(item)


if __name__ == '__main__':
    class Dummy:
        def __init__(self, value):
            self.value = value

    x = [Dummy(i) for i in range(10)]
    w = WeakOrderedSet(reversed(x))
    del w[2:8]
    assert_equals([9,8,1,0], [i.value for i in w])
    del w[0]
    assert_equals([8,1,0], [i.value for i in w])
    del x
    assert_equals([], [i.value for i in w])

有更简单的方法吗？

推荐答案

最简单的方法是利用标准库中的现有组件。

The easiest way to is to take advantage of existing components in the standard library.

OrderedDict和MutableSet ABC可以很容易地编写OrderedSet。

OrderedDict and the MutableSet ABC make it easy to write an OrderedSet.

同样，你可以重用现有的weakref.WeakSet并用OrderedSet替换它的底层set（）： / p>

Likewise, you can reuse the existing weakref.WeakSet and replace its underlying set() with an OrderedSet:

import collections, weakref

class OrderedSet(collections.MutableSet):
    def __init__(self, values=()):
        self._od = collections.OrderedDict().fromkeys(values)
    def __len__(self):
        return len(self._od)
    def __iter__(self):
        return iter(self._od)
    def __contains__(self, value):
        return value in self._od
    def add(self, value):
        self._od[value] = None
    def discard(self, value):
        self._od.pop(value, None)

class OrderedWeakrefSet(weakref.WeakSet):
    def __init__(self, values=()):
        super(OrderedWeakrefSet, self).__init__()
        self.data = OrderedSet()
        for elem in values:
            self.add(elem)

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