doc: Suggest to hash(tuple of attr) rather than XOR
Issue #28383: __hash__ documentation recommends naive XOR to combine but this
is suboptimal. Update the doc to suggest to reuse the hash() method using a
tuple, with an example.
diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index db2fa17..4adf5fa 100644
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -1409,8 +1409,12 @@
hashed collections including :class:`set`, :class:`frozenset`, and
:class:`dict`. :meth:`__hash__` should return an integer. The only required
property is that objects which compare equal have the same hash value; it is
- advised to somehow mix together (e.g. using exclusive or) the hash values for
- the components of the object that also play a part in comparison of objects.
+ advised to mix together the hash values of the components of the object that
+ also play a part in comparison of objects by packing them into a tuple and
+ hashing the tuple. Example::
+
+ def __hash__(self):
+ return hash((self.name, self.nick, self.color))
If a class does not define a :meth:`__cmp__` or :meth:`__eq__` method it
should not define a :meth:`__hash__` operation either; if it defines