input: Write a function to implement a function is_palindrome that checks if a given string s is a palindrome (reads the same forwards and backwards). If the string is a palindrome, the function should return True, otherwise it should return False.
  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]