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  1. from weakref import WeakKeyDictionary, WeakValueDictionary
  2.  
  3. class Id:
  4.     def __init__(self, key):
  5.         self._id = id(key)
  6.     def __hash__(self):
  7.         return self._id
  8.     def __eq__(self, other):
  9.         return self._id == other._id
  10.  
  11. class WeakUnhashableKeyDictionary:
  12.     def __init__(self, *args, **kwargs):
  13.         # TODO Do something to initialize given args and kwargs.
  14.         self.keys = WeakValueDictionary()
  15.         self.values = WeakKeyDictionary()
  16.  
  17.     def __getitem__(self, key):
  18.         return self.values.__getitem__(Id(key))
  19.  
  20.     def __setitem__(self, key, value):
  21.         _id = Id(key)
  22.         # NOTE This works because key holds on _id iif key exists,
  23.         # and _id holds on value iif _id exists. Transitivity. QED.
  24.         # Because key is only stored as a value, it does not need to be hashable.
  25.         self.keys.__setitem__(_id, key)
  26.         self.values.__setitem__(_id, value)
  27.  
  28.     def __delitem__(self, key):
  29.         self.keys.__delitem__(Id(key))
  30.         self.values.__delitem__(Id(key))
  31.  
  32. class Key:
  33.     __hash__ = None
  34.  
  35. d = WeakUnhashableKeyDictionary()
  36. l = [Key(), Key(), Key()]
  37. d[l[0]] = 1
  38. d[l[1]] = 2
  39.  
  40. for k in d.keys.values():
  41.     l.remove(k)
  42.     try:
  43.         print(d[Key()])
  44.         print('False match detected!')
  45.     except KeyError:
  46.         pass
Success #stdin #stdout 0.04s 9748KB
comments (?)
stdin 
Standard input is empty
stdout 
1
False match detected!
https://ideone.com/BJg7uq
language:
Python 3 (python  3.12)
created:
2 years ago
visibility:
public

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