On 9/19/2011 8:48 AM, Ethan Furman wrote:
Roy Smith wrote:
__radd__() only solves the problem if the left-hand operand has no
__add__() method itself.
Only true if the left-hand operand is so ill-behaved it doesn't check to
see if it makes sense to add itself to the right-hand operand. If it
doesn't know how, it should `return NotImplemented` -- Python will then
try __radd__ on the left-hand operand.
Also, if the right-hand operand is a subclass of the left-hand operand
then Python will try right-hand_operand.__radd__ first.
The builtin classes like int are (should be, sans bug) well-behaved.
Now, if the left-hand operand *does* know how (or thinks it does, which
could be another matter entirely), and the right-hand operand is *not* a
subclass of the left-hand operand, then you are correct -- the
right-hand operand wil not be called.
So the potential problems arise with two user classes.
--
Terry Jan Reedy
--
http://mail.python.org/mailman/listinfo/python-list
