input: Write a function to determine if a given string is a palindrome by converting all characters to lowercase and checking if the string reads the same forward and backward. If it is a palindrome return True, else return False.
  def is_palindrome(s):
    s = s.lower()
    left = 0
    right = len(s) - 1
    
    while left < right:
      if s[left] != s[right]:
        return False
      left += 1
      right -= 1
    return True
  
  assert is_palindrome("racecar")==True
  assert is_palindrome("Able was I ere I saw Elba")==True
  assert is_palindrome("python")==False
  assert is_palindrome("")==True
  assert is_palindrome("No lemon, no melon")==True
output: def is_palindrome(s):
    s = s.lower()
    left = 0
    right = len(s) - 1
    
    while left < right:
      if s[left] != s[right]:
        return False
      left += 1
      right -= 1
    return True