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copied!<h1>Attribute Tree</h1> <p>The problem with your first specification is that Python can't tell in <code>__getitem__</code> if, at <code>my_obj.a.b.c.d</code>, you will next proceed farther down a nonexistent tree, in which case it needs to return an object with a <code>__getitem__</code> method so you won't get an <code>AttributeError</code> thrown at you, or if you want a value, in which case it needs to return <code>None</code>.</p> <p>I would argue that in every case you have above, you should expect it to throw a <code>KeyError</code> instead of returning <code>None</code>. The reason being that you can't tell if <code>None</code> means "no key" or "someone actually stored <code>None</code> at that location". For this behavior, all you have to do is take <code>dotdictify</code>, remove <code>marker</code>, and replace <code>__getitem__</code> with:</p> <pre><code>def __getitem__(self, key): return self[key] </code></pre> <p>Because what you really want is a <code>dict</code> with <code>__getattr__</code> and <code>__setattr__</code>.</p> <p>There may be a way to remove <code>__getitem__</code> entirely and say something like <code>__getattr__ = dict.__getitem__</code>, but I think this may be over-optimization, and will be a problem if you later decide you want <code>__getitem__</code> to create the tree as it goes like <code>dotdictify</code> originally does, in which case you would change it to:</p> <pre><code>def __getitem__(self, key): if key not in self: dict.__setitem__(self, key, dotdictify()) return dict.__getitem__(self, key) </code></pre> <p>I don't like the <code>marker</code> business in the original <code>dotdictify</code>.</p> <h1>Path Support</h1> <p>The second specification (override <code>get()</code> and <code>set()</code>) is that a normal <code>dict</code> has a <code>get()</code> that operates differently from what you describe and doesn't even have a <code>set</code> (though it has a <code>setdefault()</code> which is an inverse operation to <code>get()</code>). People expect <code>get</code> to take two parameters, the second being a default if the key isn't found.</p> <p>If you want to extend <code>__getitem__</code> and <code>__setitem__</code> to handle dotted-key notation, you'll need to modify <code>doctictify</code> to:</p> <pre><code>class dotdictify(dict): def __init__(self, value=None): if value is None: pass elif isinstance(value, dict): for key in value: self.__setitem__(key, value[key]) else: raise TypeError, 'expected dict' def __setitem__(self, key, value): if '.' in key: myKey, restOfKey = key.split('.', 1) target = self.setdefault(myKey, dotdictify()) if not isinstance(target, dotdictify): raise KeyError, 'cannot set "%s" in "%s" (%s)' % (restOfKey, myKey, repr(target)) target[restOfKey] = value else: if isinstance(value, dict) and not isinstance(value, dotdictify): value = dotdictify(value) dict.__setitem__(self, key, value) def __getitem__(self, key): if '.' not in key: return dict.__getitem__(self, key) myKey, restOfKey = key.split('.', 1) target = dict.__getitem__(self, myKey) if not isinstance(target, dotdictify): raise KeyError, 'cannot get "%s" in "%s" (%s)' % (restOfKey, myKey, repr(target)) return target[restOfKey] def __contains__(self, key): if '.' not in key: return dict.__contains__(self, key) myKey, restOfKey = key.split('.', 1) target = dict.__getitem__(self, myKey) if not isinstance(target, dotdictify): return False return restOfKey in target def setdefault(self, key, default): if key not in self: self[key] = default return self[key] __setattr__ = __setitem__ __getattr__ = __getitem__ </code></pre> <p>Test code:</p> <pre><code>>>> life = dotdictify({'bigBang': {'stars': {'planets': {}}}}) >>> life.bigBang.stars.planets {} >>> life.bigBang.stars.planets.earth = { 'singleCellLife' : {} } >>> life.bigBang.stars.planets {'earth': {'singleCellLife': {}}} >>> life['bigBang.stars.planets.mars.landers.vikings'] = 2 >>> life.bigBang.stars.planets.mars.landers.vikings 2 >>> 'landers.vikings' in life.bigBang.stars.planets.mars True >>> life.get('bigBang.stars.planets.mars.landers.spirit', True) True >>> life.setdefault('bigBang.stars.planets.mars.landers.opportunity', True) True >>> 'landers.opportunity' in life.bigBang.stars.planets.mars True >>> life.bigBang.stars.planets.mars {'landers': {'opportunity': True, 'vikings': 2}} </code></pre>

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