On Jan 5, 1:27 am, Volker Braun <vbraun.n...@gmail.com> wrote: > Also, x.__abs__() is just the Python magic method for abs(x). The function > call syntax abs(x) will always call __abs__ and return an AttributeError if > it is not defined. So all we have is an x.abs() method that behaves exactly > like abs(x), for better or worse.
Ah, thanks. THAT's the answer I was looking for. I didn't know python had magic for abs. Indeed, '__abs__' is listed under the operators in the python doc. We're not exactly succeeding in letting the method behave exactly the same as the function, though. In plain python: >>> class A(object): ... def __abs__(self): ... return "called" ... >>> a=A() >>> abs(a) 'called' >>> class B(object): pass ... >>> b=B() >>> abs(b) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: bad operand type for abs(): 'B' Possible alternatives: * delete 'RingElement.abs'. Then any subclass that wants absolute values needs to implement __abs__ (that's necessary anyway) and, if it wants the method accessible in another form as well, also a suitable 'abs'. I could see why that's not so desirable * change 'RingElement.abs' to be a bit more intelligent in looking up the __abs__ method and throw a more informative error, such as "TypeError: bad operand type" if it's not there. * implement "RingElement.abs(self)" as "return abs(self)" to fully dispatch through python's standard channels. We're just interfacing with Python's standard machinery here. No need for extra subclasses/categories. -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To post to this group, send email to sage-devel@googlegroups.com. To unsubscribe from this group, send email to sage-devel+unsubscr...@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel?hl=en.
