On 1/24/2020 3:12 AM, Victor Stinner wrote:
IMO it's a good optimization to skip __eq__() when id(x) == id(y).
From a higher level viewpoint, what is being skipped is literally doing
'x == y'.
But
it can be surprising, so I just would like to document it somewhere.
It is, in the section on how to understand and use value comparison
*operators* ('==', etc.).
https://docs.python.org/3/reference/expressions.html#value-comparisons
First "The default behavior for equality comparison (== and !=) is based
on the identity of the objects."
Then in particular, "The built-in containers typically assume identical
objects are equal to themselves. That lets them bypass equality tests
for identical objects to improve performance and to maintain their
internal invariants."
For example, in __eq__() method documentation:
https://docs.python.org/dev/reference/datamodel.html#object.__eq
The text that follows discusses rich comparison *special methods* and
how to write them. It should refer people to the value-comparisons
section for information on specific classes, as in the second quote
above. It would not hurt if the operator section referred people back
to special method discussion. I think you should go ahead and add one
or both links.
--
Terry Jan Reedy
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