In Python, Assigning value to instace variables in list using for loop

In Python(2.7), I want to modify some of instance variables by using the instance method. For efficient coding, I tried to make a list of class variables and use for loop to assign a new value to each variable. I made an instance and ran a method but instance variables did not change. Here's the code for example.

import numpy as np

class myclass:
    def __init__(self):
        self.A = np.array([1,2,3])
        self.B = np.array([4,5,6])
        self.C = np.array([7,8,9])

    def addx(self, x): #value assigning via this method
        V = [self.A, self.B, self.C]
        for v in V:
            print(id(v))
            v = np.hstack([v,x])  # <<-- here
            print(id(v))

print('(step1)')
ins = myclass()
print(ins.A)
print(id(ins.A))

print('\n(step2)')
ins.addx(1) #value assigning in this line
print(ins.A)
print(id(ins.A))

the result (with some comments):

(step1)
[1 2 3]
47985418888576    <- (id of ins.A) 

(step2)
47985418888576    <- (id of ins.A)
47985628039168    <- (assigning step for ins.A)
47985418888896
47985628039088
47985624314064
47985628039168
[1 2 3]
47985418888576    <- (id of ins.A)

the desired result for the (step2) is

[1 2 3 1]

How can I get this result using list and for loop? Or using any other efficient way, not a repeated codes for each variables?

Additionally, i checked the id of variables. We can see that the variables in list has same id with class variables. But in the assigning step, it has a different id.