Hi, I think changing Add.__add__ to return NotImplemented is the right solution. This is the Python behavior for what you want. Python will raise an error if Add.__add__ return NotImplemented and y.__radd__(x) don't work.
There isn't any other way to do this to my knowledge. Frédéric On Wed, Jul 3, 2013 at 10:47 AM, Prasoon Shukla <[email protected]>wrote: > In Python, we have special methods that when used in a class definition, > overload standard operators. > > Now, here's the problem I am having (shown as an example): > > Let us say we have a vector - which is an instance of a class that has > been subclassed from Basic. Let's call this class Vector. Then, I have a > container class, VectMul (subclassed from Mul), that is used to hold any > objects of type *scalar * vector - *much like Mul does. I won't go too > deep into what else VectMul class does. > > Anyway, now, I have defined a method Vector.__mul__ which is supposed to > return a VectMul after performing appropriate checks on the input. > > At this point, let me just refresh your memory : if x and y are python > objects, then: > x + y => x.__add__(y) > y + x => y.__add__(x) > > Back to my question. So, when a user does: > > > - Vector*Vector, the Vector.__mul__ method will raise an error saying > that a user cannot multiply two vectors. > - Vector*scalar, the Vector.__mul__ will be called and a VectMul will > be returned. > - *scalar*Vector : *Now this is the problem - here let us say that > scalar is a Add - then the method Add.__mul__ will be called instead of > what I want to be called - in this case, Vector.__mul__ - and return a Mul > object instead of a VectMul. > > This is the problem I face right now. I googled around a bit - apparently, > we can use the __rmul__ method. But, for that to work - the Add.__mul__ (in > the third point above) should return NotImplemented (what does that even > mean? Raise an exception?). Obviously, I shouldn't have to change > Add.__add__ for this. So, how can I handle this problem? > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/sympy. > For more options, visit https://groups.google.com/groups/opt_out. > > > -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sympy. For more options, visit https://groups.google.com/groups/opt_out.
