From 509476b37085abda9c8cc0fba1451cb035e0b442 Mon Sep 17 00:00:00 2001 From: Victor Stinner Date: Mon, 19 Dec 2016 13:09:28 +0100 Subject: [PATCH] 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. --- Doc/reference/datamodel.rst | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst index b763f10eeb6..73eec1c557e 100644 --- a/Doc/reference/datamodel.rst +++ b/Doc/reference/datamodel.rst @@ -1305,11 +1305,14 @@ Basic customization Called by built-in function :func:`hash` and for operations on members of 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. + :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 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)) .. note::