Do I need "self" and "other"?

[Kurda Yon]

Hi,

I found one example which defines the addition of two vectors as a
method of a class. It looks like that:

class Vector:
  def __add__(self, other):
    data = []
    for j in range(len(self.data)):
      data.append(self.data[j] + other.data[j])
    return Vector(data)

In this example one uses "self" and "other". Does one really need to
use this words? And, if yes, why? I have replaced "self" by "x" and
"other" by "y" and everything looks OK. Is it really OK or I can have
some problem in some cases?

Thank you!