On Apr 10, 1:41 am, Simon King <[EMAIL PROTECTED]> wrote: > On Apr 10, 4:18 am, Carl Witty <[EMAIL PROTECTED]> wrote: > > > I like the "raise an exception" behavior, because it would eliminate > > questions asking why form1 and form2 below are different (from this > > sage-support > > threadhttp://groups.google.com/group/sage-support/browse_thread/thread/79d0...). > > (I have seen this exact problem at least twice on sage-support.) What > > do you think? > > I guess what i suggest wouldn't solve the plot-issue. However, i think > if one doesn't know whether an inequality holds, or if the inequality > simply makes no sense (such as in the case of an unordered field) then > bool() should neither raise an exception nor return False but return > None. I think it is much simpler to have
bool() is a Python builtin that cannot return None. bool(x) calls x.__nonzero__(); but if you try to make __nonzero__() return None, you get: <type 'exceptions.TypeError'>: __nonzero__ should return an int Chris's suggestion of making if: sometimes return an "unevaluated if" is also impossible in Python. Of course, we can (and probably should) make a new method on SymbolicEquation that returns True/False/None; we could also add support for a symbolic "unevaluated if" if we wanted. But since we use Python, we're stuck with: bool(x > 0) must return True, False, or raise an exception; and this controls what "if x > 0:" will do. Carl --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
