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Add PyObject_GenericHash() function #5
Description
Issue: python/cpython#113024
PR: python/cpython#113025
Py_hash_t PyObject_GenericHash(PyObject *obj)
It is the implementation of the default Python object hashing function object.__hash__(). In CPython it is identical to Py_HashPointer(), but has the signature compatible with tp_hash. It can only be used for Python objects, not arbitrary pointers, and it is more portable. It can be used in implementations that have no equivalence between object identity and object address.
PyObject_GenericHash() should be used for calculating the hash of Python object. Py_HashPointer() should be used for pointers not managed by Python object manger (i.e. static data, malloced data or pointers to C functions like wrapperobject.descr).
- @gvanrossum
- @encukou (prefers rename)
- @vstinner (+1)
- @zooba (prefers Petr's rename)
- @iritkatriel
Activity
encukou commentedon Jan 10, 2024
+1 on the idea. I agree with the direction this is taking us, but I feel that this direction should be noted explicitly:
This is similar to API like
Py_Isor *PyRef_Dup, which are equivalent to==/Py_IncRefon CPython, but signal that the author wants “HPy-like" semantics on implementations where they're available. IOW, this is acknowledging that HPy is a good idea :)For this function specifically, I'd prefer calling it
PyObject_HashIdentity. It should be used only for objects that are compared by identity, which doesn't sound too generic. (OtherGenericAPI is, very roughly, functions added automatically to a subclass of a built-in type.)vstinner commentedon Jan 10, 2024
+1 to add the function. Using
PyObject_GenericHash(obj)instead ofPy_HashDouble(obj)should help to make code compatible with PyPy, and other Python implementations where id() doesn't directly return an object address, but something more complicated.hodgestar commentedon Jan 10, 2024
+1 on the function too. It looks like a great idea.
Regarding the name, why not just
PyObject_Hash?fangerer commentedon Jan 11, 2024
👍
encukou commentedon Jan 11, 2024
That's a different function -- the equivalent of
hash(obj). It already exists.hodgestar commentedon Jan 11, 2024
Doh! Thanks for explaining. Now that I understand a bit better, having a function that returns a
Py_hash_tequivalent of the identity sounds very useful for C extensions and HPy. It'll give people a simple alternative to using thePyObjectpointer value as a hash.serhiy-storchaka commentedon Jan 11, 2024
On other hand, this API itself is not very useful without adding a corresponding API for
id()other thanPyLong_FromVoidPtr()and the reversed API instead ofPyLong_AsVoidPtr(). And most importantly without replacing all assignments=and comparisons==with API calls. It is too large breaking change, and I do not see it in a foresight future.As for a name, we have
PyObject_GenericGetAttr(),PyObject_GenericSetAttr(),PyObject_GenericGetDict(),PyObject_GenericSetDict(),PyType_GenericAlloc(),PyType_GenericNew()as precedence.vstinner commentedon Jan 11, 2024
I added Py_Is(x, y) function. Are you referring to that?
vstinner commentedon Jan 18, 2024
Ping @iritkatriel and @gvanrossum: what's your opinion on this API?
gvanrossum commentedon Jan 18, 2024
Looks like we're all in favor now.
vstinner commentedon Jan 19, 2024
@serhiy-storchaka: Congrats, your API is approved, you can go ahead ;-)