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

Alex A. Naanou alex.nanou at gmail.com
Fri Mar 19 13:46:07 CET 2010

Hi,

A friend of mine stumbled upon the following behavior:

---cut---

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

b + c B: adding B and C objects.

a + c C: adding C and A objects.

so far, quite logical. now let's do this:

1 + c C: adding C and int objects.

--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.

-- Alex.

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