Given a list b with a length of 12

''' Given a list b with a length of 12, output its shape. If its shape can be 
changed to n * m, output the changed array, otherwise output NO. 
[input form] integer n and m
[output form] if n * m = 12 is satisfied, the array is output, otherwise ”NO" is 
output.
[sample input]
1 12
[sample output]
[[ 1 2 3 4 5 6 7 8 9 10 11 12]]
 '''
 
new_list = []
user = input().split()
x = int(user[0])
y = int(user[1])
n = x * y
for s in range(x):
    if n <= 12:
        x_list = []
        for i in range(1, y+1):
            x_list.append(i)
        new_list.append(x_list)
    else:
        print("No")
print(new_list)

You can do it By this way also

import numpy as np
n,m=map(int,input("Enter n,m: ").split())
a=np.arange(1,13)
if n*m==a.shape[0]:
print(a)
else:
print("NO")