input: Write a function to check if a given string is a palindrome. A palindrome is a word, phrase, or sequence that reads the same backward as forward. The function should convert the string to lowercase to ignore case differences and then check if the string reads the same from both ends. If it is a palindrome, return True; otherwise, return False. If the input string is empty, consider it a palindrome by returning True.
  
  assert is_palindrome("racecar")==True
  assert is_palindrome("Racecar")==True
  assert is_palindrome("hello")==False
  assert is_palindrome("A man, a plan, a canal, Panama")==True
  assert is_palindrome("")==True
output: def is_palindrome(s):
      s = s.lower().replace(" ", "").replace(",", "").replace(".", "")
      return s == s[::-1]