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POHow can I access a deeply nested dictionary using tuples?
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copied!<p>I would like to expand on <a href="https://stackoverflow.com/questions/651794/whats-the-best-way-to-initialize-a-dict-of-dicts-in-python">the autovivification example</a> given in a previous answer from <a href="https://stackoverflow.com/users/17160/nosklo">nosklo</a> to allow dictionary access by tuple.</p> <p>nosklo's solution looks like this:</p> <hr> <pre><code>class AutoVivification(dict): """Implementation of perl's autovivification feature.""" def __getitem__(self, item): try: return dict.__getitem__(self, item) except KeyError: value = self[item] = type(self)() return value </code></pre> <p>Testing:</p> <pre><code>a = AutoVivification() a[1][2][3] = 4 a[1][3][3] = 5 a[1][2]['test'] = 6 print a </code></pre> <p>Output:</p> <pre><code>{1: {2: {'test': 6, 3: 4}, 3: {3: 5}}} </code></pre> <hr> <p>I have a case where I want to set a node given some arbitrary tuple of subscripts. If I don't know how many layers deep the tuple will be, how can I design a way to set the appropriate node?</p> <p>I'm thinking that perhaps I could use syntax like the following: </p> <pre><code>mytuple = (1,2,3) a[mytuple] = 4 </code></pre> <p>But I'm having trouble coming up with a working implementation.</p> <hr> <h1>Update</h1> <p>I have a fully working example based on @JCash's answer:</p> <pre><code>class NestedDict(dict): """ Nested dictionary of arbitrary depth with autovivification. Allows data access via extended slice notation. """ def __getitem__(self, keys): # Let's assume *keys* is a list or tuple. if not isinstance(keys, basestring): try: node = self for key in keys: node = dict.__getitem__(node, key) return node except TypeError: # *keys* is not a list or tuple. pass try: return dict.__getitem__(self, keys) except KeyError: raise KeyError(keys) def __setitem__(self, keys, value): # Let's assume *keys* is a list or tuple. if not isinstance(keys, basestring): try: node = self for key in keys[:-1]: try: node = dict.__getitem__(node, key) except KeyError: node[key] = type(self)() node = node[key] return dict.__setitem__(node, keys[-1], value) except TypeError: # *keys* is not a list or tuple. pass dict.__setitem__(self, keys, value) </code></pre> <p>Which can achieve the same output as above using extended slice notation:</p> <pre><code>d = NestedDict() d[1,2,3] = 4 d[1,3,3] = 5 d[1,2,'test'] = 6 </code></pre>

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