input: Write a function to determine if a given string is a palindrome. A palindrome is a string that reads the same forward and backward. If the string is a palindrome return True, else return False. If the given string is empty then return True.
  
  assert is_palindrome('mom')==True
  assert is_palindrome('racecar')==True
  assert is_palindrome('hello')==False
  assert is_palindrome('')==True
  
output: def is_palindrome(s):
      return s == s[::-1]