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  1. from weakref import ref, WeakKeyDictionary, WeakValueDictionary
  2.  
  3. class Id:
  4.     def __init__(self, key):
  5.         self._id = id(key)
  6.         #self._ref = ref(key)
  7.     def __hash__(self):
  8.     	# NOTE Could also be hash((self._id, id(self._ref))), but is only really
  9.     	# making a difference when entry deletion is delayed (iteration guards).
  10.         return self._id
  11.     def __eq__(self, other):
  12.         return self._id == other._id #and self._ref() is other._ref()
  13.  
  14. class WeakUnhashableKeyDictionary:
  15.     def __init__(self, *args, **kwargs):
  16.         # TODO Do something to initialize given args and kwargs.
  17.         self.keys = WeakValueDictionary()
  18.         self.values = WeakKeyDictionary()
  19.  
  20.     def __getitem__(self, key):
  21.         return self.values.__getitem__(Id(key))
  22.  
  23.     def get(self, key, default = None, /):
  24.         return self.values.get(Id(key), default = default)
  25.  
  26.     def __setitem__(self, key, value):
  27.         _id = Id(key)
  28.         # NOTE This works because key holds on _id iif key exists,
  29.         # and _id holds on value iif _id exists. Transitivity. QED.
  30.         # Because key is only stored as a value, it does not need to be hashable.
  31.         self.keys.__setitem__(_id, key)
  32.         self.values.__setitem__(_id, value)
  33.  
  34.     def __delitem__(self, key):
  35.         self.keys.__delitem__(Id(key))
  36.         self.values.__delitem__(Id(key))
  37.  
  38.     def __iter__(self):
  39.     	return map(lambda _id: self.keys[_id], self.values)
  40.  
  41. class Key:
  42.     __hash__ = None
  43.  
  44. d = WeakUnhashableKeyDictionary()
  45. l = [Key(), Key(), Key()]
  46. d[l[0]] = 1
  47. d[l[1]] = 2
  48.  
  49. print(d[l[0]])
  50. print(d[l[1]])
  51. print(d.get(l[2]))
  52.  
  53. for k in d:
  54.     l.remove(k)
  55.     try:
  56.         print(d[Key()])
  57.         print('False match detected!')
  58.     except KeyError:
  59.         pass
Success #stdin #stdout 0.04s 9624KB
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https://ideone.com/8FURDf
language:
Python 3 (python  3.12)
created:
2 years ago
visibility:
public

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