If you for some reason can’t use imports, i.e. it is a homework to do it without, following is working version of your code:
b = str(input())
k = b.split('.')
if (len(k)!=4):
print("input length is incorrect")
else:
error = False
for num in k:
if int(num)<0 or int(num)>255:
print('Error in your IP addr')
error = True
break
if not error:
print("Your IP addr is valid")
0
solved bit values from 0 to 255 for valid IP address