Class FreezableDefaultDict

Lib/importlib/metadata/_collections.py:6–25

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

# 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(typing.NamedTuple):