[Python-Dev] binary operation heuristics -- bug or undocumented? (original) (raw)

Michael Foord fuzzyman at voidspace.org.uk
Fri Mar 19 14:05:20 CET 2010

On 19/03/2010 12:46, Alex A. Naanou wrote:

[snip...]

class C(object):

... def radd(self, other): ... print 'C: adding C and %s objects.' % other.class.name ... a, b, c = A(), B(), C() 1 + c C: adding C and int objects.

That is the whole point of the radd method. ints don't know how to add themselves to C objects, so int.add will return NotImplemented and then Python will try C.radd.

All the best,

Michael

--uncut--

My first expectation would be to get a TypeError here, as ints indeed have an add method, and they do not know anything about C objects (obviously :) ). On second thought, giving client code priority to handle things has it's merits. The problem is that I found no mention of this behavior in the docs.

P.S. tested in 2.5 through 3.0 and PyPy Thanks.

-- http://www.ironpythoninaction.com/ http://www.voidspace.org.uk/blog

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