import collections # from jaraco.collections 3.3 class FreezableDefaultDict(collections.defaultdict): """ Often it is desirable to prevent the mutation of a default dict after its initial construction, such as to prevent mutation during iteration. >>> dd = FreezableDefaultDict(list) >>> dd[0].append('1') >>> dd.freeze() >>> dd[1] [] >>> len(dd) 1 """ def __missing__(self, key): return getattr(self, '_frozen', super().__missing__)(key) def freeze(self): self._frozen = lambda key: self.default_factory() class Pair(collections.namedtuple('Pair', 'name value')): @classmethod def parse(cls, text): return cls(*map(str.strip, text.split("=", 1)))