Python Index, IndexBag, Multidex

console.txt

In [1]: import index

In [2]: i = index.Multidex(unique_keys=('pk',), common_keys=('name',))

In [3]: class Person(object):
    def __init__(self, name):
        global last_pk
        self.pk = last_pk
        last_pk += 1
        self.name = name
   ...:         

In [4]: last_pk = 1

In [5]: people = [Person('Alice'), Person('Bob'), Person('Christina'), Person('Christina')]

In [6]: i.merge(people)

In [7]: i.at('pk', 1)
Out[7]: <__main__.Person at 0x1017c2490>

In [8]: i.at('name', 'Christina')
Out[8]: {<__main__.Person at 0x1017c26d0>, <__main__.Person at 0x1017c2710>}

index.py

import collections
import operator


class IndexBase(object):
    def __init__(self, key, initial=None):
        if isinstance(key, basestring):
            self.key = operator.attrgetter(key)
        elif isinstance(key, int):
            self.key = operator.itemgetter(key)
        else:
            raise ValueError('key must be a basestring or int.')

        if initial:
            self.merge(initial)

    def merge(self, items):
        raise NotImplementedError

    def add(self, item):
        self.merge([item])

    def umerge(self, items):
        raise NotImplementedError

    def remove(self, item):
        self.unmerge([item])


class Index(IndexBase, dict):
    def __init__(self, *args, **kwargs):
        super(Index, self).__init__(*args, **kwargs)

    def merge(self, items):
        for item in items:
            self[self.key(item)] = item

    def unmerge(self, items):
        for item in items:
            k = self.key(item)
            if self.get(k) == item:
                del self[k]


class IndexBag(IndexBase, collections.defaultdict):
    def __init__(self, *args, **kwargs):
        super(IndexBase, self).__init__(set)
        super(IndexBag, self).__init__(*args, **kwargs)

    def merge(self, items):
        for item in items:
            self[self.key(item)].add(item)

    def unmerge(self, items):
        for item in items:
            try:
                self[self.key(item)].remove(item)
            except KeyError:
                continue


class Multidex(object):
    def __init__(self, unique_keys=None, common_keys=None, initial=None):
        self._indicies = {}
        unique_keys = unique_keys or []
        common_keys = common_keys or []

        for key in unique_keys:
            self._indicies[key] = Index(key, initial=initial)

        for key in common_keys:
            self._indicies[key] = IndexBag(key, initial=initial)

    def by_key(self, key):
        return self._indicies[key]

    def at(self, key, val):
        return self.by_key(key)[val]

    def merge(self, items):
        for index in self._indicies.itervalues():
            index.merge(items)

    def unmerge(self, items):
        for index in self._indices.itervalues():
            index.unmerge(items)

    def add(self, item):
        self.merge([item])

    def remove(self, item):
        self.unmerge([item])