input: Write a function that takes a string and checks if it is a palindrome. A palindrome is a word, phrase, number, or other sequences of characters that reads the same forward and backward, ignoring case and spaces. If the input string is a palindrome, return True; otherwise, return False. If the input string is empty, return True. Function name should be is_palindrome.
  
  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 = ''.join(e for e in s if e.isalnum()).lower()
      return s == s[::-1]