input: Write a function to determine if a given string is a palindrome. A palindrome is a string that 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.
  assert is_palindrome("racecar") == True
  assert is_palindrome("hello") == False
  assert is_palindrome("madam") == True
  assert is_palindrome("") == True
  assert is_palindrome("a") == True
output: def is_palindrome(s):
      return s == s[::-1]