input: Write a function to determine if a given string `s` is a palindrome, meaning it reads the same backward as forward. If `s` is a palindrome return True, otherwise return False. You can assume that the input string will contain only lowercase characters and no spaces.
  assert is_palindrome('racecar')==True
  assert is_palindrome('level')==True
  assert is_palindrome('python')==False
  assert is_palindrome('madam')==True
  assert is_palindrome('')==True
output: def is_palindrome(s):
      return s == s[::-1]