[Raymond Hettinger]
> The old behavior for missing keys may have been a bug.
> Do you care about the previous behavior for deleting
> based on equality rather than equality *and* hash?
Nope, because it was neither documented nor tested, and was behavior unique
to the WeakKeyDictionary flavor of dict -- no other flavor of dict works
that way, and it was just an accident due to the __delitem__ implementation.
Note too that it's a documented requirement of the mapping protocol that
keys that compare equal must also return equal hash values.
> Python 2.3b1 (#40, Apr 25 2003, 19:06:24) [MSC v.1200 32 bit (Intel)]
> on win32 Type "copyright", "credits" or "license" for more
> information. IDLE 0.8 -- press F1 for help
> >>> class One:
> def __eq__(self, other):
> return other == 1
> def __hash__(self):
> return 1492
> >>> import weakref
> >>> wkd = weakref.WeakKeyDictionary()
> >>> o = One()
> >>> wkd[o] = None
> >>> len(wkd)
> 1
> >>> del wkd[1]
> >>> len(wkd)
> 0
Just a case of GIGO (garbage in, garbage out) to me.
> Python 2.3b1+ (#40, May 23 2003, 00:08:36) [MSC v.1200 32
> Type "help", "copyright", "credits" or "license" for more
> >>> class One:
> .. def __eq__(self, other):
> .. return other == 1
> .. def __hash__(self):
> .. return 1492
> ..
> >>> import weakref
> >>> wkd = weakref.WeakKeyDictionary()
> >>> o = One()
> >>> wkd[o] = None
> >>> len(wkd)
> 1
> >>> del wkd[1]
> Traceback (most recent call last):
> File "<stdin>", line 1, in ?
> File "C:\PY23\lib\weakref.py", line 167, in __delitem__
> del self.data[ref(key)]
> TypeError: cannot create weak reference to 'int' object
> >>> len(wkd)
> 1
> >>>
As I said the first time <wink>,
will succeed if and only if d.data has a key for a still-live object,
and that key compares equal to k1; else it will raise KeyError
(or maybe TypeError if k1 is a silly key to test in a weak-keyed dict,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
or MemoryError if we run out of memory). That's what I believe it
should do.
I didn't add "and the hash codes are the same too" because that requirement
is part of the the mapping protocol.
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