from collections import defaultdict d = defaultdict(set) assert isinstance(d['a'], set) assert isinstance(d.get('b'), set)
d['a'] is ok, and a new set object is insert to d, but d.get('b') won't. It's a bug, or just a feature? I think dict.get() method is just a *safe* version of dict[key], maybe it should be: def get(self, key, default = None): try: return self[key] except KeyError: return default
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