On 4/12/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: > > Hi there, > > many classes in SAGE implement and test for is_zero. I think these methods > > should be replaced with __nonzero__ methods, as this is the standard way > > of > > doing such a test in Python. For example, int doesn't have a is_zero(), > > such > > that one would have to test for a type (of a return value) first. > > +1, and document this in structure.element.
Comment 1: My first comment is that __nonzero__ is going to be removed from Python in Python 3000, so you should read the thread here about it being removed: http://mail.python.org/pipermail/python-3000/2006-November/004524.html (Python 3000 being the Python in SAGE is probably not as far off as you might think... I realized this at the scipy talk that Guido gave on Python 3000.) So in the future, __nonzero__ will be replaced by __bool__; currently the point of __nonzero__ is to implement bool(x) for x an object. Comment 2: One of the most important and used functions in MAGMA is "IsZero". MAGMA doesn't have an "IsNonzero". Likewise, in sage it appears in search_src('is_zero') over 200 times. This all suggests that for mathematics programming, conceptually "is zero" is the function one wants, and that moreover in writing code it is very natural to use a function called "is zero". Getting rid of is_zero and replacing it by __nonzero__ is thus not natural, since it's the opposite. I really don't like code like this: if my_complicated_number: do blah when my_complicated_number is some sort of complicated mathematical object. I much prefer if not my_complicated_number.is_zero(): do blah or even if my_complicated_number.is_nonzero(): do blah I think it's easier to read and more explicit. Comment 3: Definitely __nonzero__ (or later __bool__) should be defined whenever possible, so code like this behaves sensibly: if x: do blah Conclusions: (1) Do not eliminate the is_zero method. I.e., it should still be possible to write x.is_zero() for x an element. (2) Do implement __nonzero__, and redefine is_zero in the base to be def is_zero(self): return self.__nonzero__() (3) Make sure no derived classes define is_zero; they should instead always define __nonzero__. (4) I wish there were code to certify that derived classes don't define things they shouldn't define... William --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to [EMAIL PROTECTED] 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://sage.scipy.org/sage/ and http://modular.math.washington.edu/sage/ -~----------~----~----~----~------~----~------~--~---
