Error in code NameError: name ' ' is not defined

[ppman00]

Hi. I have a problem with code(self studying-just started).
I have a problem "NameError: name 'numb' is not defined".
It should be easy solution for that and im sitting with it about 2 hours.

my code:

from typing import List, Any, TextIO

 
lista: List[int] = []

file = str(input("file name: ")+'.txt')

n = int(input("give how many digits u want to input, modulo 4 must be 0: \n", ))

while n % 4 != 0:
    n = int(input("wrong", ))
print("give " + str(n) + " digit")

while len(lista) < n:

    digit= int(input("give digit: "))

    if not 0 <= digit <= 9:
        print('wrong')
    else:
        lista.append(digit)

print(lista)

m = int(len(lista)/4)

#print(m)

for i in range(0, m):

    x = i
    y = i + 1

    numb.x=int(str(lista[0 + i*4]) + str(lista[2 + i*4]))
    numb.y=int(str(lista[1 + i * 4]) + str(lista[3 + i * 4]))

    numb.i= (numb.x) + (numb.y)

    chr(a.i)
    print(chr(a.i), end=" ")

file: TextIO = open((file), 'w')
file.write(chr(a.i))
file.close()