"method involving two objects" is that possible in Python?

Jason Scheirer jason.scheirer at gmail.com
Fri Jun 27 23:52:07 CEST 2008


On Jun 27, 2:41 pm, Kurda Yon <kurda... at yahoo.com> wrote:
> Hi,
>
> I just started to learn Python. I understood how one can create a
> class and define a method related with that class. According to my
> understanding every call of a methods is related with a specific
> object. For example, we have a method "length", than we call this
> method as the following "x.length()" or "y.length()" or "z.length()",
> where z, y, and z are objects of the class.
>
> I am wandering if it is possible to create a method which is related
> not with a single object (as in the previous example) but with a pare
> of objects. For example, I want to have a class for vectors, and I
> want to have a methods which calculate a dot product of two vectors.
> One of the possibilities is to use __mul__ and that I calculated dot
> product of "x" and "y" just as "x * y". However, I am wandering if I
> can declare a method in a way that allows me to calculate dot product
> as "dot(x,y)".
>
> Thank you in advance.

def dot(x, y):
  ...

class Vector:
  __mul__ = dot

or

class Vector:
  def __mul__(x, y):
     return dot(x, y)

You can refer to the function defined as dot, assuming dot(x, y)
returns some vector z. The first argument (x) will be bound to self in
either case in any Vector instance.



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