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, the function should return True; otherwise, it should return False. If the input string is empty, the function should return True.
  
  def is_palindrome(s):
      '''Returns True if the string s is a palindrome, False otherwise.'''
      return s == s[::-1]
  
  assert is_palindrome("racecar")==True
  assert is_palindrome("hello")==False
  assert is_palindrome("level")==True
  assert is_palindrome("")==True
  assert is_palindrome("a")==True
output: def is_palindrome(s):
      return s == s[::-1]