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copied!<p>Is this usage appealing to you?</p> <p>Easy look-up and usage of single entries:</p> <pre><code>>>> left("10000") Entry({'parent': '10001', 'key': '10000', 'fkey': 'asdf'}) >>> left("10000")['key'] '10000' >>> left("10000")['parent'] '10001' </code></pre> <p>Easy look-up of parents:</p> <pre><code>>>> left("10000").parent() Entry({'parent': '', 'key': '10001', 'fkey': 'qwer'}) >>> left("10000").parent().parent() >>> left("10001") Entry({'parent': '', 'key': '10001', 'fkey': 'qwer'}) >>> left("10001") is left("10000").parent() True </code></pre> <p>Easy look-up of related entries:</p> <pre><code>>>> left("10001").related() Entry({'parent': '', 'key': 'qwer', 'fkey': '10001'}) >>> right("qwer") Entry({'parent': '', 'key': 'qwer', 'fkey': '10001'}) >>> right(left("10001").related()['key']) Entry({'parent': '', 'key': 'qwer', 'fkey': '10001'}) >>> right("qwer") is left("10001").related() True </code></pre> <p>Particularly here is the example in your question: parent's foreign key:</p> <pre><code>>>> left("10000").parent()['fkey'] 'qwer' </code></pre> <p>If so, then here is the code! Classes:</p> <pre><code>class Entry(object): def __init__(self, dataset, d): self.dataset = dataset self.d = d def parent(self): return self.dataset.parent_of(self) def related(self): if not self.dataset.related_dataset: raise ValueError("no related dataset specified") return self.dataset.related_dataset(self['fkey']) def __getitem__(self, k): return self.d.__getitem__(k) def __repr__(self): return "Entry(%s)" % repr(self.d) def __str__(self): return str(self.d) class Dataset(object): def __init__(self, data): self.data = dict((k, Entry(self, v)) for (k,v) in data.items()) self.related_dataset = None def set_related_dataset(self, dataset): self.related_dataset = dataset def entry(self, key): if isinstance(key, Entry): return key return self.data[key] def __call__(self, key): return self.entry(key) def parent_of(self, entry): entry = self.entry(entry) if not entry['parent']: return None return self.data[entry['parent']] </code></pre> <p>And the usage for the data you've provided:</p> <pre><code>leftdata = {'10000': { 'key': '10000', 'fkey':'asdf', 'parent':'10001'}, '10001': { 'key': '10001', 'fkey':'qwer', 'parent':''},} rightdata = {'asdf': { 'key': 'asdf', 'fkey':'10000', 'parent':'qwer'}, 'qwer': { 'key': 'qwer', 'fkey':'10001', 'parent':''}} left = Dataset(leftdata) right = Dataset(rightdata) left.set_related_dataset(right) right.set_related_dataset(left) </code></pre> <p>Explanation: Wrap each dict value in an <code>Entry</code> class with <code>__getitem__</code> defined to make it usable as a dict (more or less). Have a <code>Dataset</code> class that maps primary keys to these <code>Entry</code>s. Provide the <code>Entry</code> access to this dataset and provide convenient methods <code>.parent()</code> and <code>.related()</code>. In order for <code>.related()</code> to work, set which dataset the "related" one should be with <code>set_related_dataset</code> and it all ties together.</p> <p>Now you can even just pass <code>Entry</code>s and you'll be able to access the related entries without needing to pass both datasets in.</p>

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