Hi Eric, On 2015-02-22, Eric Gourgoulhon <egourgoul...@gmail.com> wrote: > Yes that's conversion, but both 0+x and x+0 works because, I think, of=20 > lines 979-990 of=20 > sage.structure.coerce.pyx: > # Allow coercion of 0 even if no coercion from Z > if is_Integer(x) and not x and type(yp) is not type: > try: > return yp(0), y > except Exception: > self._record_exception() > > if is_Integer(y) and not y and type(xp) is not type: > try: > return x, xp(0) > except Exception: > self._record_exception() > ... > so that both x+0 and 0+x works:
Seriously? I didn't know that Sage's coercion model has such special cases. OK, it makes it possible to get a typical usecase with least effort. But my impression is that ultimately such special cases cause a lot more confusion than a clear model in the spirit of "arithmetics across parents relies on coercion morphisms, which are canonical morphisms in suitable categories, and the composition of coercion morphisms is a coercion morphism". Note this: sage: from sage.rings.integer import is_Integer sage: is_Integer(int(0)) False I guess that explains why "0+x+y" works on the command line but not in a python module, and why "sum([x,y])" doesn't work either. Best regards, Simon -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
