How to make a function associated with a class?

[Kurda Yon]

Hi,

I have a class called "vector". And I would like to define a function
"dot" which would return a dot product of any two  "vectors". I want
to call this function as follow: dot(x,y).

Well, I can define a functions "dot" outside the class and it works
exactly as I want. However, the problem is that this function is not
associated with the class (like methods a method of the class).

For example, if I call "x.calc()" or "y.calc()", python will execute
different methods if "x" and "y" belongs to different classes. I want
to have the same with my "dot" function. I.e. I want it calculates the
dot product ONLY IF the both arguments of that function belong to the
"vector" class.

Is it possible?

Thank you in advance.