numeric emulation and __pos__
tjreedy at udel.edu
Tue Jul 8 23:17:52 CEST 2008
Ethan Furman wrote:
> Anybody have an example of when the unary + actually does something?
> Besides the below Decimal example. I'm curious under what circumstances
> it would be useful for more than just completeness (although
> completeness for it's own sake is important, IMO).
All true operators and some built-in functions translate to special
-x == x.__neg__() == type(x).__neg__(x) == x.__class__.__neg__(x)
What should happen to '+x'? Raise SyntaxError? Ignore the '+'? Or
translate it to __pos__ in analogy with '-' and __neg__? Guido made the
third choice: partly for consistency perhaps, but also for the benefit
of user-written classes. Decimal started as user-contributed decimal.py.
Does anything else use this hook? I don't know, but I do know that
there are periodic demands for *more* operators for user use. So I
expect it has been.
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