[Python-Dev] RE: [Python-checkins] python/dist/src/Lib weakref.py,1.19,1.20 (original) (raw)

Tim Peters tim_one@email.msn.com
Sun, 25 May 2003 02:48:25 -0400

[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 "", 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 ,

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.