input: Write a function to determine if a given string is a palindrome. A string is considered a palindrome if it reads the same backward as forward. The function should return True if the string is a palindrome and False otherwise. If the input string is empty, the function should return True.
  def is_palindrome(s):
      '''Write your code here.'''
  
  assert is_palindrome('racecar')==True
  assert is_palindrome('hello')==False
  assert is_palindrome('madam')==True
  assert is_palindrome('')==True
output: def is_palindrome(s):
      return s == s[::-1]