Like os.path().join() , how Obj.method().method().. class source code written?

Eg
import os
os.path.join()

For normal case

class A:
   def add(self,x,y):
      return x+y
obj_a = A()
print(obje_a.add(1,2))

What should I write so that it will give me option for method after add

I am not sure if I understand what you want to do.

It looks like you want to call a method on an object returned by a method. There is nothing preventing you from doing that. In your example code obj_a.add(1, 2) returns and object of type (class) int. Of course you can call one of the methods of int:

class A:
   def add(self, x, y):
      return x + y

obj_a = A()
print(obj_a.add(1, 2).as_integer_ratio())