zope:queryMultiAdapater

おそらく/usr/lib64/python/site-packages/zope/interface/adapter.pyのこれなんだろう。

    def queryMultiAdapter(self, objects, interface, name='', default=None):
        factory = self.lookup(map(providedBy, objects), interface, name)
        if factory is not None:
            return factory(*objects)

        return default

これだけではたいしたことはわからない。なんか検索して戻って来るのはfactoryで、そいつにinterfaceを満たすobjectのインスタンスを生成させている。なのでlookupの実装と、lookupの実装で探しているコンテナを特定し、InterfaceをregisterするAPIを読み解かないといけない。

class AdapterLookup(object):
    # Adapter lookup support
    # We have a class here because we want to provide very
    # fast lookup support in C and making this part of the adapter
    # registry itself would provide problems if someone wanted to
    # persistent adapter registries, because we want C slots for fast
    # lookup that would clash with persistence-suppplied slots.
    # so this class acts a little bit like a lookup adapter for the adapter
    # registry.

    def __init__(self, registry, surrogates, _remove):
        self._registry = registry
        self._surrogateClass = registry._surrogateClass
        self._default = registry._default
        self._null = registry._null
        self._surrogates = surrogates
        self._remove = _remove

問題のlookup.

    def lookup(self, required, provided, name='', default=None):
        order = len(required)

        if order == 1:
            # Simple adapter:
            s = self.get(required[0])
            byname = s.get(provided)
            if byname:
                value = byname.get(name)
            else:
                value = None

            if value is None:
                byname = self._default.get(provided)
                if byname:
                    value = byname.get(name, default)
                else:
                    return default
                
            return value

orderが0ってことはrequieredは[]とか()だ。どういう状況なのだろうか？

        elif order == 0:
            # null adapter
            byname = self._null.get(provided)
            if byname:
                return byname.get(name, default)
            else:
                return default

getが取り出す操作を担当。ここにあるのはどれがbest matchかを決める実装

        # Multi adapter

        with = required[1:]
        key = provided, order

        for surrogate in self.get(required[0]), self._default:
            byname = surrogate.get(key)
            if not byname:
                continue

            bywith = byname.get(name)
            if not bywith:
                continue

            # Selecting multi-adapters is not just a matter of matching the
            # required interfaces of the adapter to the ones passed. Several
            # adapters might match, but we only want the best one. We use a
            # ranking algorithm to determine the best match.

            # `best` carries the rank and value of the best found adapter.
            best = None
            for rwith, value in bywith:
                # the `rank` describes how well the found adapter matches.
                rank = []
                for rspec, spec in zip(rwith, with):
                    if not spec.isOrExtends(rspec):
                        break # This one is no good
                    # Determine the rank of this particular specification.
                    rank.append(list(spec.__sro__).index(rspec))
                else:
                    # If the new rank is better than the best previously
                    # recorded one, make the new adapter the best one found. 
                    rank = tuple(rank)
                    if best is None or rank < best[0]:
                        best = rank, value
            # If any match was found, return the best one.
            if best:
                return best[1]

        return default

method weakrefはweakrefだろう。なぜ使っているのか理解するべし。
なぜsurrogateなのか

    def get(self, declaration):
        if declaration is None:
            return self._default

        ref = declaration.weakref(self._remove)
        surrogate = self._surrogates.get(ref)
        if surrogate is None:
            surrogate = self._surrogateClass(declaration, self._registry)
            self._surrogates[ref] = surrogate

        return surrogate