How do you check if a given input is a palindrome?

Question

I need to check if the input is a palindrome.

I converted the input to a string and compared the input with the reverse of the input using list slicing. I want to learn a different way without converting input to a string.

def palindrome(n):
   num = str(n)
   if num == num[::-1]:
      return True

Answer 1

Assuming that n is a number, you can get digits from right to left and build a number with those digits from left to right:

n = 3102
m = n
p = 0
while m:
     p = p*10 + m%10 # add the rightmost digit of m to the right of p
     m //= 10 # remove the rightmost digit of m

print(p) # 2013

Hence the function:

def palindrome(n):
    m = n
    p = 0
    while m:
         p = p*10 + m%10
         m //= 10
    return p == n 

Note that:

if num == num[::-1]:
    return True

will return None if num != num[::-1] (end of the function). You should write:

if num == num[::-1]:
    return True
else:
    return False

Or (shorter and cleaner):

return num == num[::-1]