input: Write a function to identify if a string s has matching parentheses. If the string contains properly matched parentheses, return True; otherwise, return False. If the string is empty, return True.
  
  assert matching_paren("()")==True
  assert matching_paren("(())")==True
  assert matching_paren(")(())")==False
  assert matching_paren("((())")==False
  assert matching_paren("")==True
output: def matching_paren(s):
      stack = []
      for char in s:
          if char == '(':
              stack.append(char)
          elif char == ')':
              if not stack:
                  return False
              stack.pop()
      return len(stack) == 0