[Python-Dev] 2.5 status (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Mon Aug 7 16:55:24 CEST 2006

tanzer at swing.co.at schrieb:

The code (exception handler added to demonstrate and work around the problem):

try : h = hash(p) except OverflowError, e: print type(p), p, id(p), e h = id(p) & 0x0FFFFFFF prints the following output: <type 'instancemethod'> <bound method ScriptCategory.isapplicable of_ _<ScriptMenuMgr.ScriptCategory object at 0xb6cb4f8c>> 3066797028 long int too large to convert to int This happens with Python 2.5b3, but didn't happen with Python 2.4.3. I assume that the hash-function for function/methods returns the id of the function.

No (not really). Instead, it combines the hash of the target object with the address of the function object. The hash function of the method object, in itself, cannot raise this overflow error.

However, it involves hash(p.im_self). So if Script_Category.hash is implemented as you show below, this error might occur.

>>> class X(object): ... def hash(self): return id(self) ... >>> hash (X()) Traceback (most recent call last): File "", line 1, in OverflowError: long int too large to convert to int

Yes, this comes from id() now always returning positive integers, which might be a long if the object pointer is > MAXINT

I think both instance_hash and slot_tp_hash should be changed to just truncate long ints to the range LONG_MIN..LONG_MAX

Notice that this error could have occurred already in 2.4, on a 64-bit system where sizeof(void*) > sizeof(long) (i.e. on Win64).

Regards, Martin

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