[Python-Dev] Problems with new-style classes and coercion (original) (raw)

Guido van Rossum guido@python.org
Mon, 22 Apr 2002 12:47:06 -0400

Python 2.2 (#28, Mar 13 2002, 23🔞18) [MSC 32 bit (Intel)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> coerce >>> class ex(object): ... def init(self, v): ... self.v = v ... def coerce(self, other): ... return self, ex(other) ... def add(self, rhs): ... return ex(self.v + rhs.v) ... def repr(self): ... return 'ex(' + repr(self.v) + ')' ... >>> ex(3) ex(3) >>> coerce(ex(1),2.3) (ex(1), ex(2.2999999999999998)) >>> ex(1).add(ex(2)) ex(3) >>> ex(1)+2.3 Traceback (most recent call last): File "", line 1, in ? File "", line 9, in add AttributeError: 'float' object has no attribute 'v'

New-style classes don't support coerce. It's a long and sad story, but basically coerce was a mistake, and I've stopped supporting it for new-style classes. This means that the + operator doesn't call coerce. For some reason, coerce() still calls it; maybe that was a mistake.

--Guido van Rossum (home page: http://www.python.org/~guido/)