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A defaultdict that can be frozen after which it will not add new missing keys but still return a default object
from collections import defaultdict
class freezable_defaultdict(dict):
def __init__(self, default_factory, *args, **kwargs):
self.frozen = False
self.default_factory = default_factory
super(freezable_defaultdict, self).__init__(*args, **kwargs)
def __missing__(self, key):
if self.frozen:
return self.default_factory()
self[key] = value = self.default_factory()
return value
def freeze(self):
self.frozen = True

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@barahilia barahilia commented Jan 9, 2019

An alternative is to use defaultdict.get(key, default_value), which doesn't add a new entry for a missing key in defaultdict

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